Introduction to Fish Biology~25,000 species described

- most numerous group of vertebratesapproximately 45%-50% of all vertebrate species are fishdominant life form in almost all aquatic systemsmany diverse adaptations to life -

a very interesting group for biologiststhe potential of many species as a food source -

a valuable resource worth studying for knowledgeof management and harvest strategies

Fish Phylogeny -several diverse evolutionary lines are lumped together andcommonly called fishes

Common characteristic of fishescraniumbackbone, live in water, possess gills throughout life,if they have scales or armor they are dermal

or they are descended from ancestors with scales or armor,

Fish ClassificationPhylum Chordata

have notochord at some time in their lives, have a post-anal tailat some time, dorsal tubular nerve cord, have gill slits,pharyngeal basket,

Subphylum Vertebrata all groups have vertebrae surrounding nerve cord, cranium

Class Myxini - hagfishesClass Cephalaspidomorphi - lampreys

lampreys and hagfishes often lumped into Class Agnatha no jaws, skel. of cartilage, persistent notochord

All groups from this point on have jaws and paired appendagesClass Chondrichthyes - cartilaginous fishessharks, skates, rays,jaws, paired appendages, skeleton of cartilage,

All groups from this point on have a skeleton with boneClass Osteichthyes - bony fishes

bony skeleton, operculum, swimbladderAll groups from this point on have four legs or

are derived from species with four legsClass Amphibia - amphibians

All groups from this point on have amniotic developmentClass Mammalia - mammals

All groups from this point on have a unique connection between the neck and skullClass Reptilia - reptilesClass Aves - birds

Myxini, Cephalaspidomorphi, Chondrichthyes, and Osteichthyesare collectively called fishes,

all are vertebrates with gills throughout life and live almostexclusively in water - lack four legs

Statistics on fishesNumbers of species

hagfish - 20 spp - marine scav + predatorslampreys - 35 spp - fw + marine, parasitic and filter feeders

within the Chondrichthyessharks - 400+ spp - mostly large marine pred, some in freshwaterrays + skates - 300+ spp. - most marine, size 10cm to 7mchimaeras - 30 sp - strange mostly deepwater species -

Teleostomes (Osteichthyes) - 20,000 sp and, 40% of all vertebrateswithin this groupSarcopterygians - lobefins - fleshy bases on paired finslungfishes - 6 sp - fw 1 Aus, 1 S.A, 4 Afrcoelocanth - 1 sp - Latimeria - only in Indian Ocean

once thought extinct - 1938 fisherman captured onean extinct Sarcopterygian gave rise tetrapod lineage

Actinopterygians - ray finned fishes -Chondrosteans - sturgeons (23), paddlefish (2), bichirs (10)Neopterygians -Amiiformes - bowfin (1) Semionotiformes - gars (7) (mostly freshwater)Teleosteans - most species

every aquatic habitatlakes, streams, desert springs, caves, seas from pole to pole,deep seas both off and on the bottom,within this group there is gradation in body forms from primitiveto advanced (soft-rayed, spiny rayed)

most of our familiar species heretarpon, eels, shad, salmon, piranhas, minnows, suckers,cod, topminnows, silversides, sea horses, mullets,perch, bass, gobies, remoras, scorpionfish, sculpins,flounders, puffers, boxfish, etc.

The major lineages of fishes are very oldThe agnathans have a history that goes back 500 myby 400 mya all the major lineages represented and others thathave gone extinct

So modern groups, although all are called fish are verydistantly related and separated by approximately 400 my of evolution

Within all this diversity58% are marine41% are freshwater1% euryhaline

within euryhaline species anadromous - move upstream to spawn (temperate zone)catadromous - move downstream to spawn (tropics)

Questions Why is there so much diversity in freshwater?Why do species move into alternate habitats to spawn?Why are there anadromous forms in the temperate zones and

catadromous forms in the tropics?

Most marine species are coastalonly 13% of all fish species live exclusively in open ocean44% live in less than 200m of water, near the coastwhy?

Most fish species are found in the tropics (both fw and marine)why?

In spite of diversity - we don't have any trouble recognizing mostthings that are fish -

One thing that all fishes have in common is that they live in waterand living in water imposes some constraints on them that theymust live within - the properties of water limit the numberof morphological, physiological, and ecological options for fishes

Water is dense - 800 x airbenefits - 1. Buoyancy - little or no effect of gravity

2. allows more force to be exerted on itcosts - resists movement

most fish are streamlined - those that must movequickly, or over long distances

most fish have a large proportion of the body asmuscle for locomotion -

Water is almost incompressiblemoving through air involves compression and displacementmoving through water - all displacement

this produces turbulence and dragbenefit -displacements are detectable -

gives long-distance sense of touch allows fish to detect other fish and prey

allows for suction feeding and ventilationwater can be sucked into, and pumped out of mouth forcefully

Slight compressibility of water -sounds move further and faster - 4x faster than airfish don't have external ears, but nearly all fish can heara fish body is nearly the same density as watersound waves pass readily through fish bodies

use internal structures (otoliths) of different densityand swim bladders to intercept sound waves

all hear and many can make sounds and use them forcommunication

Water is a good solvent -dissolved solutes necessary for aquatic life as nutrientscreates a problem -

fish must resist being dissolved themselves - having theirsolutes lost by diffusion, or in conditions of high salinitylosing their water through osmosis - later

one additional factor makes this problem a special problem -oxygen is not very soluble in waterair is 21% O2water is 0.8% O2 (8ml/l, or 12.8 mg/l) max. solubility decreases with increases in temperature and salinitycan limit fish activities,to compensate, fish have a large portion of the surfacearea of their bodies very permeable - the gillsfor extracting oxygen, but also provides an easy entryand exit point for solutes and water

Water has low light penetration1000 m max (pure water)most fish in lighted zone (productive zone)most fish live in a relatively murky and dark environmentcompensate through highly developed sense of touch,smell, some have electric organs (fields that can be usedto detect movements) or electric sense to detect the weak electric charge of other living things, some make their own light

The biology of fishes is the biology of active living organismsin water. The properties of water limit and shape the biology of fishes.