Coolie Mae's Ichthyology Notes

Ichthyology Notes: Lecture One

Ichthyology
- study of fishes
  - Why fishes and not fish?
    - Fishes is the plural for multiple species of fish, while fish is plural (and singlular) for a single species
- There are more fishes than any other vertebrate group
  - about 25,000 living species have been described
    - still being described
Major Groups of Fishes
- Phylum Chordata
  - Subphylum Vertebrata
    - Fishes (indeed vertebrates) can be divided into two major lines (Superclasses) that diverged at least 400 million ybp (years before present)
    - Superclass Agnatha
      - line with the most ancestral characters
      - represented today by about 80 species of hagfishes and lamprey
        
        Class Myxini (hagfishes)
        Class Cephalaspidomorphi (lamprey)
        *Class Pteraspidomorphi (heterostraci)
        *extinct
    - Superclass Gnathostomata
      - vertebrates with jaws
      - Gnathostomata used to be divided into two Grades
        
        Pisces: "true fishes"
        tetrapods
        this system has been discarded due to the polyphletic nature of Pisces
      - Today systematists recognize three grades
        
        Grade Placodermiomorophi
        
        contains the extinct placoderms
        a sister group to both cartilaginous and bony fishes
        to 6m, but most much smaller
        large predators, such as coccosteus
        also referred to as "arthrodires"
        
        Grade Chondrichthiomorphi
        
        contians the cartilaginous fishes
        Class Chondrichthyes
        cartilaginous fishes are split into
        
        Subclass Elasmobranchii
        
        Sharks, skates, and rays
        greater than 800 species
        
        Subclass Holocephali
        
        Chimaeras and ratfishes
        approximately 30 species
        
        Grade Teleostomi
        
        contians all other fishes and the tetrapods
        divided into three classes
        
        Class Acanthodii
        
        extinct group
        mid and surface water feeders
        freshwater and marine
        earliest know true-jawed fishes
        most <20cm with the longest being to 2.5m
        often with paired spines between pectoral and pelvic fins
        
        Class Sarcoptergyii
        
        contains the coelacanth, lungfishes, and tetrapods
        
        Subclass Coelacanthimorpha
        
        contains Gombessa
        one extant species Latimeria chalumnae
        
        marine
        lives off Mozambique
        group thought to be extinct
        found in 1938
        live bearing
        to 1.8m
        
        Subclass (unnamed)
        
        Infraclass - lungfishes
        
        3 families with six species
        
        four species are in Family Protopteridae (African lungfishes)
        
        Subclass Tetrapoda
        
        Class Actinopterygii
        
        ray-finned fishes
        divided into two subclasses
        
        Subclass Chondrostei
        
        contains two orders of early bony fishes
        
        Acipenseriformes
        
        sturgeons and paddle fishes
        
        Polypteriformes
        
        bichirs and reed fishes
        
        Subclass Neopterygii
        
        contains two ancestral orders
        
        Amiiformes: bowfin
        Semionotiformes: gars
        
        and all other Orders are in the Division Teleostei
        
        i.e. more than 24000 species of fishes
        
        the recent bony fishes
Despite their swimming ability, most fishes are "surface oriented"
- 97% of water is in the oceans
- < 1% is found in lakes and streams
- the rest is found in the atmosphere, polar caps, groundwater, etc.
- yet only about 58% of fishes are marine
- about 41% are freshwater
- about 1% utilize both environments
- reasons for the distribution deal with use of surfaces and evolutionary processes (higher probability with isolation)
- most of the marine environment is open ocean
  - only the surface is lit
  - rest is rather unproductive
  - only about 13% of marine fishes live in open ocean
    - Breakdown of 13%
      - 1% epipelagic
      - 5% unlit, deepwater pelagic
      - 7% deepwater, benthic fishes
  - 78% of marine fishes live in < 200m of water
  - live along narrow bands around land masses where productivity is high
History of Ichthyology
- Aristotle (384 BC) was the first known ichthyologist
  - recognized about 150 species
  - recognized that some fishes change sex (not studied again until mid-20th century)
- Until the mid-20th century, ichthyology was about describing the fishes of the world and hypothesizing about their evolutionary relationships
- Today, many ichthyologists are in the fields of physiology, ecology, behavior, or their interfaces
- Two of the most important ichthyologists were Americans
  - David Starr Jordan (1851-1931)
    - described North American fishes and their evolutionary relationships (Also the founding President of Stanford University)
  - Carl L. Hubbs (1894-1982)
    - Jordan's last graduate student
    - work was largely systematic
    - published about 1/2 page for everyday he lived! (around 16,000 pages of published material)

Basic Fish Anatomy

gross external anatomy
Form
- Generalized shape is fusiform
  - i.e. torpedo-shaped
  - ideal for hydrodynamics
    - reduces drag
    - greatest cross-section is about 36% of length from the anterior end
- globiform (globe-like) fishes
  - tetraodontids: puffers
- anguilliform (eel-like) fishes
  - anguillids: eels
- filiform (thread-like) fishes
  - serrivomerids: saw tooth eels
- compressed fishes
  - side-to-side
- depressed fishes
  - dorsal-to-ventral
Body Covering
- Fishes are covered with a relatively tough skin
- skin is continuous with the linings of body openings and covers the eye
- for most fishes, scales develop in the skin
- scales often indicate much about the ecology of a fish and characterize major groups of fishes
  - agnathans typically lack scales
  - sharks and their relatives typically are covered with placoid scales
    - much like teeth in that they are covered with enamal, have a denine layer, and a pulp cavity
    - thought to improve the hydrodynamic efficiency of swimming
  - the scales of bony fishes evolved independantly
    - layered plates, with bone as one of the layers
    - ganoid scales represent the ancestral condition
      - e.g. Lepisosteidae (gars)
  - teleost fishes have elasmoid scales
    - cycloid scales
      - round, flat, thin scales
      - e.g. salmonids (trout and salmon), cyprinids (carp, minnow, shinners, darters), clupeids (sardines, herring)
    - ctenoid scales
      - similar to cycloid scales, but have ctenii on the posterior(exposed) region of the scale
      - ctenii are small, comb-like teeth or projections
        
        convergent evolution is involved
        
        many unrelated fishes evolved ctenii
        
        thought largely due to hydrodynamic efficiency
- Interesting Adaptations
  - Armor - scales modified into large, bony plates
    - e.g. loricariid catfishes - armored suckermouth catfishes
    - syngathids - pipefishes and seahorses
  - fast swimmers often have smaller scales
    - e.g. salmonids
  - some of the fastest swimmers are scaleless
    - e.g. xiphiids such as xiphas
    - most tuna appear scaleless, but have deeply embedded scales
  - finally, many bottom-dwelling fishes are scaleless
    - e.g. cottid - sculpins
    - ictalurids - North American catfishes
    - some eels
    - some cartilaginous fishes
      - e.g. dasyatids - stingray, except as modified into spines
Appendages - cirrhi and fins
- cirrhi are flaps of flesh
- fins are classified as median or paired
  - median fins
    - dorsal fins: back
      - bony spinous and soft dorsal fins
      - continuous e.g. Lepomis -sunfishes
      - multiple condition e.g. Stizostedion - walleye
      - bare spines e.g. gasterosteus - stickleback
      - adipose fin e.g. oncorhynchus - salmonids
      - finlets e.g. thunnus - scombrinds - tuna
    - Caudal fin: tail
      - Proterocercal (diphycercal)
        
        body axis is continuous with the caudal fin
        
        divided roughly equally into dorsal and ventral parts
        e.g. Petromyzon - lamprey
      - Heterocercal
        
        body axis is upturned caudally
        supporting caudal fin primarily on ventral element
        
        e.g. cartilaginous fishes: sturgeon
        
        abbreviated heterocercal - ancestral bony fishes
        
        e.g. gar
      - Homocercal
        
        body axis terminates with a fusion product, the urostyle
        this structure helps support the caudal fin rays
        
        i.e. the body axis does not run through the caudal fin
        
        homocercal caudal fin is found in most teleost fishes
    - Anal fin
      - fin behind the vent
      - sometimes modified into a sex organ for copulation and internal fertilization (male)
        
        e.g. gonopodium of Gambusia belonging to the family Poeciliidae
  - Paired Fins
    - Pectoral fins (Psub1)
      - supported by the pectoral gridle that joins the skull
      - often situated higher than the pelvic fins
      - lacking in some fishes
        
        e.g. hagfishes
      - modified in others
        
        e.g. flying fishes - Exocoetidae
        e.g. flying gurnards - Pactylopteridae
    - Pelvic fins (Psub2)
      - typically supported by a pelvic gridle anchored in the belly musculature
      - position varies tremendously
        
        Psub2 are abdominal in more ancestral fishes
        
        e.g. clupeids, salmonids, cyprinids
        
        Psub2 are thoracic in other groups
        
        e.g. Centrachids: basses, sunfishes e.g. cichlids: bass-like fishes of Africa and Central and South America
        
        advanced (anterior to) the Psub1, in some fishes
        
        e.g. callionymids: dragonets
        
        finally, Psub2 are jugular in some fishes
        
        e.g. blennids: blennies
        
        other fishes never evolved them
        
        hagfishes and lamprey
        
        or lost them
        
        e.g. anguillids and other eels
  - Fin supporting structures in bony fishes are called fin rays
    - Spines - unsegmented, uniserial structures
    - Soft rays - typically segmented, often branched, and always biserial
      - may be present in any fin, but follow spines if spines are present
      - compose the rays of all caudal (tail) fins in bony fishes
    - Spinous soft ray
      - soft rays acting as spines
        
        we find them in the Cyprinidae, e.g. Cyprinus: carp
        also found in Ictaluridae, i.e. North American catfishes
      - some soft ray elements have fused embryonically and provide for the spinous soft ray
Openings
- mouth, gill apartures (including spiracle in some fishes), and the vent (anus and urogentital openings) are the principle gross openings in fishes
  - Mouth
    - may be terminal or at the end
      - superior
      - subterminal
        
        slightly overhung by the snout
      - inferior
        
        ventral
    - bordered by lips
      - membranous for most fishes, to fleshy and papillose
      - e.g. some catostomids (suckers)
      - scaleless and sensory, but in sharks and their relatives lips are covered with placoid scales that become abruptly enlarged as teeth
  - gill aperatures
    - bony fishes have a single opening on either side of the head
    - normally anterior to the P1 fin base
    - usually covered with an operculum
    - exceptions
      - e.g. ogcocephalids - batfishes
        
        opening is behind P1 base and lacks an operculum
      - hagfishes: 1-16 external gill openings/side
      - lamprey: 7 external gill openings/side
      - nearly all sharks: 5 external gill openings/side
      - skates and rays: 5 external gill openings/side
      - many cartilaginous fishes also have a spiracle
        
        outside opening to the pharyngeral cavity
  - Anus: anus and vent
    - on the midventral line of the body
    - usually found on the 2nd half of total length
      - rarely anterior
      - e.g. Aphredoderus: pirate perch
        
        jugular in position
      - sharks and lungfishes
        
        anus opens into a depression
        cloaca "sewer"
      - in most fishes the openings of the urogential ducts are in the vent, posterior to the anus
  - Abdominal Pores
    - some sharks and lampreys
    - ancestral character
    - communication between body cavity and the outside
      - normally paired: one on each side of the ventral midline
      - thought to be vestigal exits for eggs and sperm
      - lost in more derived fishes
  - Nares
    - dirhinous condition is usual
    - one or two nostrils on either side of the head
    - leads to a blind sac for olfactory sense
    - lamprey and hagfishes have a monorhinous condition
      - a single, median naris
    - most fishes have nares in a dorsal lateral position
    - elasmobrachs(sharks, skates, rays) have nares that are ventrolateral
    - narial aperatures have a diverse anatomy
      - groove-like opening - e.g. dogfish Squalus
      - partial division of the nares
        
        makes an incurrent and excurrent naris - e.g. rajids
      - separate pore for each current in most teleosts
Anatomy in relation to buoyancy
- specific gravity of freshwater is about 1.0005
  - specific gravity = ratio of the weight or mass of a substance with an equal volume of another substance
    - e.g. distilled water for fluids
- specific gravity of seawater is about 1.026
- specific gravity of fish flesh is about 1.076
- neutral to near-neutral buoyancy is achieved by fishes in four main ways:
  - Storage of low-density compounds
    - e.g. sharks
      - most sharks have a large liver
      - site of lipid storage
      - most s.g. approximately 0.86 - 0.92
    - a few teleosts also store lipids
      - mostly triglycerides
      - bone is the site of storage
        
        e.g. Rockfishes - Sebastes Scorpaenidae
  - Hydrodynamic lift while swimming
    - e.g. most free-swimming sharks
      - heterocercal tail and positive attack angles of P1 and head create lift
  - Heavy tissue (e.g. muscle and bone) reduction
    - typical of fishes that live in the bathypelagic zone
      - characterized by unfavorable trophic(feeding) conditions
        
        "harsh" environment
      - "lethargic" fishes
        
        move little compared to fishes in the mesopelagic above
        i.e. energy conservation
      - bathypelagic fishes may thus benefit in terms of buoyancy and in not using resources to make heavy, "expensive" tissues
  - Gas Bladders (or Swimbladder) incorporation
    - most common way of adjusting buoyancy
      - most teleost fishes
    - makes a low density, gas-filled space
    - advantageous over the last three methods
      - does not restrict activity as does reduced tissues
      - gas can be adjusted relatively rapidly to respond to changes in buoyancy due to changes in depth, temperature, salinity, etc.
      - "invention" of the bony fishes

The Gas Bladder

Two Types:

Physostomous gas bladder

has a connection (duct) between the bladder and the gut
typical of more ancestral teleosts
- e.g. clupeids, salmonids, ictalurids
bladder inflation is by gulping air

results in relatively surface oriented fishes

this method would be impossible for deep water fish due to Boyle's Law
- i.e. volume of a gas changes inversely with pressure
  - e.g. Each ten meters of water 1 atm

Depth (m)	Fraction	vol (cc)
00	1	1000
10	1/2	500
20	1/3	330
30	1/4	250
40	1/5	200

Physostomous gas bladders are deflated by a "gas-spitting reflex"
- duct connecting with the gut is controlled by sphincter muscles
- internal pressure causes the sphincter to open
  - gas is released
  - fish sinks

Second type of gas bladder is the physoclistous
- typical of more derived teleosts
  - about 2/3 of teleosts
- closed bladder
- gas inflation is due to a gas gland and rete mirabile("wonderful net")
- rete mirabile
  - a counter-current exchange(multiplier) mechanism
  - made from the capillaries supplying blood to and away from the gas bladder
  - afferent (toward) capillaries and efferent (away) capillaries run in opposite directions
  - close enough (approximately 1 micron) for diffusion of gases
- Partial pressure of O2 (Pr. O2) is about 0.2 atmospheres in saturated arterial blood of fishes
  - higher concentration of lactate at the gas gland
    - product of metabolism
    - also CO2 + H2O >>> H2CO3 (carbonic acid) >>>diassociates>>> H+ +HCO3- (bicarbonate ion)
  - oxyhemaglobin becomes acid hemaglobin when loaded with H+
    - a change in quaternary structure of the hemaglobin occurs with the H+ loading
      - oxygen unloads into blood
      - diffuses into the gas bladder
      - continues through efferent capillaries
      - diffuses to afferent capillaries along its length
      - O2 concentration may reach 300 atmospheres
    - release of gas is due to the oval organ
      - a thinned region of the gas bladder
      - capillary complex is separated from the bladder lumen by one-cell layer of epithelium
      - area surrounded by a sphincter that controls the rate of gas absorption
      - pneumatic duct of physostomes and the oval organ of physoclists are homologous

Gas bladders in relation to distribution and ecology of fishes
- most wide-spread function of the organ is buoyancy
- many stream fishes (e.g. darters [Percidae]) have lost the gas bladder
  - evolutionary adaptation to strong current repeatly and independantly has lead to the loss of the gas bladder
- Mesopelagic (200-1000m) fishes have well-developed gas bladders
  - e.g. Lanternfishes: Family Myctophidae
    - make long, nightly, vertical migrations feeding on plankton
    - best examples of physoclist anatomy
    - variations in depth are from 3m at night to 400m during day
- Bladder is lost for bathypelagic fishes (1000m-4000m)
- gas bladders appear again in deep water fishes near the bottom
  - zones of food concentration
    - benthic invertebrates
    - accumulated products from the surface
  - about 50% of these fishes have gas bladders
- Physoclists predominate the marine environment
- many physoclists are also found in freshwater
- physostomes predominate in flowing freshwater (lotic environments)
- Other Functions of Gas Bladders
  - Respiratory organ
    - temporary organ of respiration
    - aerial respiration
    - some fishes have a highly sacculated or an alveolan lining in the gas bladder
    - utilize O2 in air; many are facultative air breathers (conditional status)
      - e.g. Gars(Lepisosteidae), bowfin(Amiidae), bichirs(Polypteridae)
  - Sound reception
    - density of fish flesh is close enough to sea water that the fish is essentially "transparent" to sound
      - except for bone and the gas bladder
        
        these provide acoustical discontinuities based on greater differences in density with water
        
        results in sound conductors and resonators
  - In many fishes an anterior extension of the gas bladder touches head bones near the inner ear
    - e.g. gadids(cod), sparids(porgies), clupeid(herrings and sardines)
    - the largest category making up the Division Teleostei is the Superorder Ostariophysi
      - includes cyprinids(minnows, shiners, carp, darters, etc.), catfishes, and characins(tetras)
      - the ostariophysi have a set of paired bones that make up the "Webarian apparatus"
        
        connects the gas bladder with the inner ear
        volume changes in the bladder cause ossicles to move
      - vibration is transmitted to the labyrinth, the seat of sound reception
  - Sound production
    - aquatic habitat is noisy!
    - Some species of fishes are noisy
      - stridulation with teeth, spines, bones (rubbing on part with another)
      - hydrodynamic - pressure waves from swimming movements
      - gas bladder - striated muscles originate on the dorsal body wall and insert on the gas bladder
        
        make a drum of the bladder when they vibrate

Lecture Two

Regulation of temperature in fishes
- most fishes are poikilothermic
  - i.e. they have body temperatures similar to their surroundings, and they are not adjusting body temperature
- some fishes are ecotherms and can regulate their temperature
  - Behavioral thermoregulation
    - non-random movements towards or away from warmer or cooler temperatures
    - temperature may affect metabolism
      - enzymes have narrow ranges of optimal working temperatures
        fishes that select particular temperatures may benefit through more efficient physiology
        e.g. sockeye salmon Oncorrhynchus nerka
        select warm water when digesting food
        shallow, about 15 degrees C
        
        select cooler water at other times
        deeper, about 5 degrees C
  - Physiological thermoregulation
    - exhibited by continuously swimming fishes
      - e.g. tuna:Family Scombridae; white shark; Family Lamnidae
    - they are endothermic
      - they conserve the heat from metabolism
        i.e. from large muscle masses that are continuously contracting
      - the higher-than-ambient temperature increases diffusion of O2 by myoglobin
      - results in greater swimming preformance
        i.e. warm muscle contracts faster than cool muscle
        fishes utilizing physiological thermoregulation are typically large predators
      - they use heat-exchanging retia mirabilia(plural)
        due to counter-current flow of blood
        cool blood is heated as it approaches the muscle mass
        warm blood leaving the muscle mass loses its heat to the incoming blood in adjacent blood vessels
        results in heat conservation
      - endothermic fishes do not have constant body temperature
      - temperature is still largely determined by the environment
        large fishes such as tuna may overheat
        swimming patterns may help
Respiration
- Efficient oxygen uptake and delivery is vital in fishes due to the low O2 concentration of water
  - water contains roughly 1/30 as much O2 as the atmosphere above it
- Various tissues, especially the yolk sac, serve as temporary respiratory membranes in fish embryos
  - any thin, highly vascular surfaces
- after hatching, P1 are highly vascular while developing and assist developing gills
  - sometimes temporary opercular vascularization occurs in Amia (bowfin, amiidae)
- gills are the main site of gas exchange for most fishes
- Gills
  - bony or cartilaginous arches
    - each arch has two rows of gill filaments
      - i.e. a holobranch
    - a single row filaments is called a hemibranch
    - each filament is covered with gill lamellae
    - gas exchange efficiency is maximized by a countercurrent exchange mechanism
    - regulation of oxygen uptake
      - some fishes, e.g. Oncorhychus mykiss can "recruit" lamellae with activity
        i.e. the regulate O2 uptake by regulating blood flow
      - fishes can also change the position of the filaments
        i.e. regulate water flow
        the hemibranchs are moved such that pressure in, and possibly also flow from, the oral cavity is regulated
        strong abduction of the hemibranchs results in "coughing"
        coughing usually "clears" the gill lamellae of detritus, etc.
        results in a violent sweeping of water over the gills
- Air-breathing fishes
  - many have modified gills
    - e.g. Clarias - "walking catfishes"
      - have a branched, bulbous, dendritic structure
        "respiratory tree" in a suprabranchial cavity
      - allows uptake of atmospheric O2, distribution in hypoxic water, and increased dispersal ability
        Clarias moves on land typically at night during rain
  - Climbing perches Anabas
    - have a "labyrinth organ"
      - in a suprabranchial cavity
    - creep on land by use of P1 and movable, spiny, opercular covers
  - Skin
    - known that fishes have some "dermal respiration" but its function is poorly understood
    - usually occurs as a "cutaneous respiration"
      - i.e. the ability matches the O2 demand of the skin
        e.g. Ictalurus melas - black bullhead
        skin is a minor respiratory organ which supplies approximately 5% of O2 demand
  - Mouth
    - Electric eels, Electrophorus, are obligate air breathers
      - they drown if kept immersed
      - highly vascular buccal cavity
        air is held as a bubble
        most O2 requirements are met
        mouth is highly modified
        many papillae
        increase in surface area
        
        gills are degenerate
        eels come up at approximately 1 minute intervals for air
  - Gut
    - highly vascularized, thin membranes of the gut are used in O2 uptake from swallowed air
      - e.g. Plecostomus Loricariidae
        "flatulent fishes"
        gills are still used
  - Gas Bladder
- Oxygen Requirements
  - Vary with the species
    - e.g. minimum of 5-6mg/L O2 for salmonids
    - yet only 3mg/L O2 for some ictalurids
  - larger fish consume more oxygen than smaller fish
    - e.g. mg/Hr
      - but smaller fish consume more when biomass-indexed
        e.g. mg/g/Hr
  - Responses to hypoxic conditions
    - typical first response to hypoxic conditions includes
      - increase in ventilation rate
        e.g. opercular beats/min
      - initial increases are followed by dramatic decreases in ventilation rate and O2 consumption
        e.g. Oncorhynchus(salmonid),Lepomis(centrarchid),Ictalurus(ictalurid)
      - a short term response of decreasing metabolism is likely adaptive
        i.e. these fishes are oxyconformers
        i.e. they adjust metabolism to local oxygen condition
      - mahi mahi are an example of oxyregulators
        i.e. they work harder and harder to pull out the same amount of oxygen in hypoxic conditions
        they maintain a constant O2 consumption
        even to the point of death
Reproduction
- Primary sexual characteristics
  - reproductive glands - gonads
    - testes - male
    - ovary - female
    - ovotestes - simultaneous hermaphrodites
  - gonads are internal, and longitudinally positioned
    - usually suspended by mesenteries(membranes) from the roof of the coelomic cavity
    - usually positioned near the kidneys and gas bladder
  - both ovaries and testes are typically paired structures
    - yet ovaries often fuse and form a single ovary
  - testes - to about 12% of body weight
  - ovaries - to about 70% of body weight
  - gonadal-somatic index is a good clue to seasonal reproduction in fishes
    - note, however, only on a gross scale
    - Gonadal Somatic Index(GSI) = (Gonad weight / total fish weight) x 100
    - plot GSI as a function of time and "spawning season" can be discovered
      - "spawning season" may be human invention
    - scale of GSI varies with species
    - GSI is a gross measure of fecundity
      - fecundity = # of offspring produced by an individual
        usually indexed as the number of eggs in the ovaries of female
      - fecundity generally increases with the length of a fish
      - the length-fecundity relationship is easily derived by a simple linear regression (on log transformed data)
    - e.g. Centropygae potteri: ripe ovary at approximately 6% of body weight, while the testes are ripe at approximately 2% of body weight
- Centropygae is iteroparous
  - i.e. repeated reproductive events
    - daily basis
  - iteroparity is usually selected in unpredictable environments
    - advantageous in that losses are only a fraction of reproductive effort
    - the greater the iteroparity (i.e. # of spawns) the smaller the fraction
- the extreme opposite of iteroparity is semelparity
  - "big bang" reproduction
  - all eggs in one "environmental basket"
  - e.g. Oncorhynchus pacific salmon
    - spawn and die
  - selected in stable, predictable environments
Review of Gametogenesis
- Spermatogenesis
  - spermatogonia grown in seminiferous tubule walls
  - "stock" is kept through mitosis
  - grow into primary spermatocytes(diploid)
    - undergo 1st meiotic division
      - results in to secondary spermatocytes
        undergo the 2nd meiotic division
        results in four haploid spermatids
        
        Note: sperm usually develop in spermatocysts (i.e. pockets of spermatocytes surrounded by sertoli cells
  - spermatids are associated with sertoli cells which transfer nutrients to them as the spermatids transform into sperm
    - head (nuclear material, acrosome)
    - middle piece (mitochondria rich)
    - tail (flagellum)
  - classification of Teleost testis status based on germinal epithelium
    - Regressed: only spermatogonia
    - Early Maturation: germinal epithelium is in a state of continuous spermatogenesis (spatially) to the periphery of the seminiferous tubule
    - Mid-maturation: seminiferous tubule is dicontinuous near ducts; continuous to periphery
    - Late-maturation: tubule is discontinuous to periphery
    - Late-maturation prior to regression: scattered spermatogonia only, spermatogenesis has ceased, germinal epithelum consists largely of sertoli cells
- Oogenesis
  - a stock of oogonia is maintained in the germinal epithelium of the ovary by mitosis
  - an oogonium grows into a primary oocyte (diploid)
  - the primary oocyte undergoes the 1st meiotic division
    - produces secondary oocyte and a polar body
  - potentially each of these undergoes a 2nd meiotic division
  - which would result in an ootid and a polar body from the secondary oocyte
  - the polar body would produce two more polar bodies
  - the ootid grows into an ovum
- folliculogenesis occurs during oogenesis
  - i.e. developing oocytes receive nutrients from surrounding follicle cells
    - oocytes develop in a follicle
  - during the 1st meiotic division (prophase I of meiosis; pachytene to diplotene) the oocyte pinches off from the germinal epithelium
- Fecundity interpretation
  - fecundity-fertility relationship
    - i.e. fertility: the number of eggs fertilized is a much better estimator of reproductive success
    - not all eggs may be fertilized
    - many eggs may not even be spawned
      - especially for iteroparous species
  - Fecundity of multiple spawners
    - requires knowledge of fecundity of individual spawning acts
      - plus the temporal pattern of reproduction
  - Fecundity of fishes with different types of investment in offspring
    - e.g. most fishes are oviparity: lay eggs
    - many fishes (e.g. scorpaenids) have lecthotrophy (ovoviviparity): hold eggs inside
    - many fishes (e.g. widespread in elsamobranchs, poeciliids, 14 families) have viviparity: nourished inside the mother (matrotrophy)
  - General rule:
    - more care (energy allocation) to an individual offspring, the fewer offspring that are produced
    - larger offspring (or parental care) may increase the probability of survival
  - What is the potential advantage of high fecundity?
    - G.C. Williams suggests highly fecund organisms can make rapid genetic adjustments to environmental change
      - they "purchase" more "lottery tickets" in an uncertain world
      - more eggs equal more lottery tickets
  - Fecundity and fish size relationship
    - not only do larger females produce more eggs
      - they may produce larger eggs
      - larger eggs represent greater investment per offspring
  - Fecundity and environment
    - increased food may lead to higher fecundity and/or larger eggs
    - e.g. Abudefduf abdominalis Hawaiian Sergent Major (Mao Mao)
      - increased food = increased clutch
  - Difficulty in determination of optimal reproductive tactic (summary)
    - Semelparity may have the highest fitness in predictable environments
- Alternative reproductive strategies and tactics
  - strategy = genetic & tactic = conditional
  - another way that fishes optimize investment in reproduction
    - e.g. Leponis macrochirus - bluegill sunfish
      - males nest in colonies
      - females choose amoung males/nest sites
      - males compete for nest sites
        larger males are favored
      - alternative mating strategies/tactics have evolved
        three types of males
        Parental
        large & older
        delayed reproduction
        
        Sneaker
        small & young
        
        Satellite male (aka female mimic)
        slowly lowers onto the nest while male and female are spawning
        older sneakers
        early reproduction
      - Sex change in fishes
        sex change refers to a functional change from one gender to the other
        sex determination is the problem of going from a juvenile to a gender
        plasticity in sex determination does not equal sex change
        
        Hermaphroditism
        Simultaneous - i.e. both male and female function (usually alternating)
        e.g. hamlets, serranidae
        
        Sequential
        mature male >>> mature female (protandry or protandrous sex change)
        e.g. Pomacentridae & Sparidae
        
        mature female >>> mature male (protogyny or protogynous sex change)
        very common, about 20 families
        
        Many fishes are territorial-haremic
        i.e. they live in territories
        
        as opposed to systems in which all males come from sex-changed individuals
        i.e. monandric systems
        e.g. some pomacanthid angelfishes
        
        finally, there is unisexuality in fishes
        all female species
        reproduce through parthenogenesis
        more appropriately called gynogenesis
        e.g. Poecilia formosa Poeciliidae
        thought to have evolved from a hybrid of two closely-related species
        still "use" sperm of ancestral species to stimulate development of the eggs
        no genetic material is exchanged
        
        sexual parasite?
        potentially a mutalism (depends on circumstances)
        females may copy the mate choice of other females
        if ancestral species females choose the "parasitized" male due to the "mate choice" of the gynogen, then the relationship may be mutualistic
Sensory Perception
- fishes have a diversity of senses
- Chemoreception
  - includes detection of odors and tastes
    - highly different in sensitivity than for terrestrial animals
    - the sensitivity of olfactory and gustatory(taste) organs are much the same in fishes
      - mostly distinguished by location and by different processing centers in the brain
    - olfactory receptors are found in olfactory pits(or sacs)
      - nares lead to the pits
      - water flow through the pit is accomplished by
        cilia
        movement of branchial pumping
        swimming
        combinations of the above

Lecture Three

Aspects of Ethology
- most fishes are non-migratory
  - i.e. they stay in a homerange or territory
  - home ranges are undefended
    - only areas where the fish lives
  - territories are defended
- Convex polygon method of homerange or territory determination
  - Haphazardly choose a focal individual
  - Determine length of observation period
  - mark with flags until area over observation reaches an asymptote
- Another technique is similar for territorial fishes but employs the use of model bottles
  - often used in ecological studies
  - measurements are taken of the relative distance that the model is attached by a territorial species
  - general result is conspecifics are attacked furthest away than congeuers, confamilials, etc.
Migration
- more or less continuous movement from one location to another
- usually includes a return to a starting location
- temporal patterns vary
  - diel (daily): e.g. feeding [Myctophidae], spawning [Labridae:wrasses]
  - lunar or seasonal: spawning [Serranidae: basses]
  - lifetime: spawning [salmonidae]
- Terms used in migration
  - potamodromy: movement in streams (e.g. catastomids moving upstream to spawn)
  - limnodromy: movement in lakes (e.g. Stizostedion spawning shoals)
  - oceanodromy: movement in marine environments (e.g. temperate clupeids moving north when warm, south when cooler)
  - diadromy: movement between fresh and marine waters
    - anadromy: adults moving from a marine to freshwater environment (e.g. salmonids)
    - catadromy: adults moving from a freshwater to marine environment (e.g. anguillids)
    - amphidromy: free movement between both environments (e.g. some carangids)
  - Homing of salmon Oncorhynchus is probably the best studied example of migration in fishes
    - recognize the odor of their natal stream
      - become imprinted during a critical period as juveniles
      - differentiate stream branches as they ascend the stream for spawn (on the return trip)
Shoaling(schooling)
- an estimated 25% of fishes that shoal, shoal throughout life
- about 50% of all fishes shoal during some times their lives
  - often in juvenile stages
    - important anti-predator behavior
- shoal: a group of fish(es) that are mutally attracted to each other
  - excludes aggregation for other reasons
    - e.g. topography, food resource
  - aggregations are nonpolarized; fish have a more or less random orientation to each other
  - schools are polarized; all fish are oriented in the same direction and move at the same speed
- Vision is very important in shoal maintenance
  - most shoals disperse at night
  - schooling fishes have an opomotor reaction
    - fish swims at a given speed and thus "stops" the relative movement of the bars
    - opomotor reaction, if fixed on a neighbor would maintain speed for schooling
- distant touch (i.e. detection of pressure waves) may maintain distances
- Potential Benefits and Costs
  - increased hydrodynamic efficiency
    - (+)boost from vortices made by the fish ahead
    - (+)less drag due to mucous slough of the fish ahead
    - (-)spread of disease by mucous
  - predation
    - (+)reduced risk of predation
      - focus on an individual difficult
      - reduced individual risk with numbers
    - (-)increased risk for less than average individual?
  - (+)increased efficiency of food finding
  - (-)increased competition for food found
  - (+)increased reproductive success by available mates
  - (-)increased competition for mates?
- schools of bait fish often "boil"
  - fish from the perimeter of the school dive inward and toward the surface
  - thought to lower the probability that the individual will be taken
    - also a reason to stay in a group
    - known as the "selfish herd" hypothesis
Agression
- behavior associated with aggression is called aganistic behavior
  - includes both sides of behavior
  - e.g. chase and flee; not just chase
- Aggression is usually escalated
- ritualized behavior - noncontact displays - have an evolutionary advantage
  - i.e. they are less costly
- escalation starts with displays, then nips, fin ripping, and finally death if injury is great enough
  - most constest end early, often after displays
    - Betta Belontiidae
- when fighting occurs, it is presumed that the cost of fighting, on the average, is less than the benefit
- Fighting is context related
  - e.g. Coryphaena hippurus Mahi Mahi
    - thought not to fight over food
    - yet it depends on distribution of food
- Other Factors in Aggression
  - Prior residence
  - Size
  - Previous Encounters
Fishes Rest
- Day and Night Communities of fishes
  - Presumably for energy conservation
  - Much needed area of research
Communication
- Vision
  - The most important sense for finding food and communicating for most fishes
  - Pigments are found in chromatophores
    - Primarily in the dermis
      - irregularly star-shaped cells
    - capable of relatively rapid color changes
      - color changes involve both hormones
        e.g. steriod hormones
        e.g. color changes in wrasses
      - Neurotransmitters are also important (e.g. acetylcholine)
        e.g. more rapid changes such as those involved with aggression
    - Two Main Purposes in Coloration
      - Communication and Evasion of predators
        color patters may be a balance between selection forces
        e.g. Endler's work with guppies
        females prefer bright mates (e.g. more spots & red spots)
        so do predators
    - Types of Color Patterns
      - Red - red wavelengths of light are filtered out at moderate depth (>10m)
        hard to see (cryptic)
    - Eye Spots (ocelli)
      - usualy a dark spot surrounded by a light ring
      - often at the base of the caudal peduncle
        other locations too
      - thought to misdirect the attack of predators
    - Bars and Stripes
      - Vertical and horizontal orientation, respectively
      - both serve as a form of disruptive coloration
        i.e. colors or patterns that disrupt outlines
        thus individuals are harder to see
      - bars are typical of fishes that move through plants
        e.g. centrarchids and cichlids
      - movement causes "flicker fusion"
        i.e. individual outlines may be lost as bars and vertical obstructions blend
      - stripes are typical of shoaling fishes
        individual outlines are lost as the stripes blend together
    - Countershading - common in fishes
      - dark from above
      - light from below
    - Eye Ornamentation - similar to the ocellus problem
      - eye is thought to be a focal point for predators
      - often disguised by bars or stripes or fields of spots
    - Special Patterns
      - egg spots in males of mouthbrooding cichlids
        on the anal fin
      - cleaner fish advertisment colors
      - "Poster Colors"
        Bright, flashy colors
        may actually be cryptic on coral reefs
        may be aposomatic coloration, "warning coloration"
      - nonrandom behavior is usually the result of communication
      - often investigated with contingency tables
        
        Signal Response
        Stare Move to Kitchen Attacks
        Stare 2 0 0
        "Go to Kitchen" 0 6 2
        Attacks 1 8 0
      - Data is analyzed to see if nonrandom patterns occur in the distribution of diads
      - typically using G-test or chi^2 test for independence
  - Auditory Signals
    - Balistids(triggerfishes) - ridges on teeth for stridulation
    - Ariids(sea catfishes) - rough spines that rub in sockets
    - Sciaenids - muscles on the gas bladder
    - note, sound may be an influential prezygotic isolating mechanism
      - e.g. Notropis minnows, cyprinids & Lepomis, centrarchids
  - Chemical Signals
    - Semiochemicals - affect growth, health, behavior or population biology of another individual or species
    - Interspecific
      - Allelochemics
        Allomones - benefit sender
        Kairomones - benefit reciever
    - Intraspecific
      - Pheromones
        Releasers: result in an immediate response
        Primers: influence physiology (e.g. reproductive state)
        slower time scale
    - Schreckstuff - "fear scents" aka "alarm substance"
      - found in the superorder Ostariophysi
        e.g. freshwater minnows, catfishes, characins, etc.
      - special "club cells" are found in the epidermis
        contain the schreckstuff odor
        only released upon damage to the skin
        reactions vary
        faster swimming, slow swimming, increased sheltering, etc.
        Alarm reaction
      - Can be considered an allomone, kairomone, and pheromone
Ecology of Fishes
- important in managing natural resources, e.g. fisheries
- protecting threatened and endangered species
- as model systems to answer basic questions about ecological processes
- present patterns of fishes in space are thought to be the result of a series of "filters"
  - Zoogeographic filter - coarsest
    - global scale
    - determines where fishes are found due to large physical barriers
      - e.g. mountain ranges, oceans, geological events(glaciers), etc.
      - note that zoogeographic barriers can also occur on smaller scales
        e.g. waterfalls
  - Environmental filters
    - temperature, salinity, DO, pH, etc.
  - Biotic filters
    - species may be excluded from an area due to biotic interactions
      - e.g. predators, competitors, parasites, diseases, etc.
  - The environmental filters usually determine the fundamental niche of a species
    - n-dimensional hypervolume - the fundamental ecological niche
  - The zoogeographic and biotic filters largely determine the realized niche
- the assemblages of fishes living together at the same time and place is a fish community
  - interactions between species lead to "interlocking realized niches"
    - i.e. the community is often thought to be in some form of equilibrium
    - i.e. an equilibrium or deterministic community
  - altering any part of the community may disrupt the whole community
  - the equilibrium or deterministic community has the following characteristics
    - persistence - structure does not drift much through time
    - resilience - the structure is not by change, original structure returns after perturbation
    - extensive habitat and resource partitioning within the community
    - species are morphologically divergent from each other
  - An alternative to this model is the nonequilibrium or stochastic community
    - thought to form in unpredictable environments
    - population desities are usually too low to be regulated by biotic factors
    - high overlap in resource utilization occurs
    - Doherty developed the "recruitment limitation hypothesis"
      - postulates that the supply of larvae to a coral reef is usually so low and random, that densities at which interspecific competition would start are rarely, if ever, reached
    - stochastic and deterministic communities represent extremes on a continuum
Conservation Issues
- Succession is a natural part of change in ecosystems
  - species, entire communities, come and go
  - key issue is the rate of change
- Human-induced changes to aquatic environments
  - exploitation - fisheries
    - overfishing
    - can result in elimination of fishable stocks
      - e.g. sardines once plentiful off CA
    - often extended influences into terrestrial ecosystems
      - e.g. anchoveta fishery collapse off Peru, which caused a collapse in sea bird populations
    - is the result of overexploitation reversible?
      - depends on regulation of community structure
        e.g. nonequilibrium communities may not rebound
  - Introduction of nonnative species
    - often introduced to "improve" local fish communities
      - often backfires, and has just the opposite effect
        e.g. nile perch Lates introduction in Lake Victoria (collapse of community structure)
    - hybridization is another problem
      - closely related species may hybridize
      - may lead to the loss of diversity
    - Habitat alteration
      - Dams, channels, urban areas, pollution
      - habitat is altered abruptly
      - thousands to millions of years of selection may be meaningless
Life history is complicated
vitellogenesis
bear live young
sexually dimorphic
6-18 month life span
early 3/4 ; late 6/7
internal fertilization, modified anal fin
store sperm capable ; gravid spot
3/7 reproductive events depending on length of summer season
temp begins and sunlight % ends
longer standard length means more embryos
Predation: smaller with predators
females are more likely to eat their own
prey selection varies with native/introduced habitat, season,availabity,competition, prey risk
technology dna, microsatellite

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Signal	Response
	Stare	Move to Kitchen	Attacks
Stare	2	0	0
"Go to Kitchen"	0	6	2
Attacks	1	8	0

Lab One Pictures(ichthy1.exe) Lab Two Pictures(ichthy2.exe) Lab Three Pictures(ichthy3.exe)

Lab One Pictures(ichthy1.exe)
Lab Two Pictures(ichthy2.exe)
Lab Three Pictures(ichthy3.exe)