Internal Physiology of FishesChapter 8

March 2009

FeedingMost fishes are carnivores.

plankton feedersdemersal feedersopen water predators

Bony fishes – teeth can be found in jaw, roof of the mouth, on gill rakers, and in pharynx

Cartilaginous fishes – teeth only on jaw margin

Gill rakers & arches

Digestive Systemmouthpharynxesophagusstomach

J-shaped or elongated

intestineanterior pyloric

caeca secretes digestive enzymes

receives inputs from pancreas and liver

spiral valvecloaca/anus

Circulatory System

Fish have a two-chambered heart.Deoxygenated blood is pumped to the gills where

gas exchange occur.

Circulation and Heat ExchangeMost fish are

poikilothermic.Few large sharks and

bony fish can maintain core body temperature slightly higher than their environment.

rete mirabile (‘wonderful net’)

adaptation for inhabiting colder waters

Respiratory AnatomyFish exchange O2 and CO2 through paired

gills.

Cartilaginous fishes Bony fishes

Respiratory Anatomy – Cartilaginous vs. Bony Fishes

Cartilaginous FishesMost swim continuously.First pair of gill slits is

modified into spiracles.Usually 5 gill slits – may

have 6 or 7.

Bony FishesHave a single common gill

chamber.Covered by an operculum

Respiratory AnatomyCovered by an

operculumGill archesGill filamentsLamellae

Gas exchange occurs by simple diffusion

Countercurrent system of flow

Osmoregulationregulation of the

body’s internal salt balance

Bony fish Body fresher than

seawater Drink seawater Salt excreted by

kidney Small amount of urine Chloride cells

Cartilaginous fish Rectal gland Urea in blood Absorb water through

gills

Nervous SystemFish possess a central nervous system,

consisting of a brain and spinal cord.

Variation exists. Proportional size of the lobes reflects the predominant movement and feeding behaviors of particular species. (i.e. the largest area of the lamprey brain is the cerebellum and medulla which indicates the fishes reliance on grasping with its jaw and attaching to its food).

Fish SensesSmell – use sensory cells in olfactory sacs on both

sides of the head. Each sac opens to the nostrils or nares.

During dissection, note the large portion of the forebrain devoted to smell particularly in the shark.

Fish SensesTaste – Taste buds can be found on the

mouth, fins, skin, lips, and barbels of fish.

Fish SensesSight – used by most fishes

Unlike terrestrial vertebrates, fish eyes focus by moving the lens closer or farther away from the subject

Shallow water species have color vision

● Sharks and deeper water species may have little color vision, but see best in contrasting light situations

● Some have a nictitating membrane that can cover the eye from the bottom to reduce brightness or offer protection

Fish SensesTouch – fish possess a lateral line consisting

of canals in the skin and in the bone or cartilage of the head that connect to neuromast cells that are sensitive to vibration.

Fish SensesHearing – perceive

sound waves with their inner earsUse fluid filled canals on

either sides of the brainSome fish amplify

sounds using their swim bladder

Involved in balance – use ear stones or calcified otoliths that rest on sensory hairs

Fish Skeleton

Shark Skeleton

ReproductionSexes are usually separate.Some fish are hermaphroditic, but usually

still reproduce with other individuals.Some fish are sequential hermaphrodites –

individuals begin life as one gender and later change into the other.

Sexually dimorphic sockeye salmon (male on bottom)

Simultaneous HermaphroditesFish in the Salmon and Sea bass families.

Protygynous sequential hermaphroditism

Protandrous sequential hermaphroditismInitial phase: initial males and females

Terminal phase: males

Fish Reproductive AnatomyJawless and bony fish – separate urogenital

opening for urination and gamete releaseCartilaginous fish – duct leads from

reproductive organ to the cloaca

http://www.marinebiodiversity.ca/shark/english/skull5.htm

Reproductive behaviorTiming of reproduction controlled by sex

hormones released into blood stream.In response to maturation of gametes or to

environmental cuesPotential mates come together.CourtshipFertilization – may be internal (most

cartilaginous fish) or external (most bony fish)

Some fish tend eggs or brood nests (usually males)

Early Development Oviparous – large number of immature eggs

are laid at a single time. Larval fish hatches quickly, but still retains and absorbs yolk sac.

Ovoviviparous – female retains eggs inside her reproductive tract for protection

Intrauterine cannibalism

Viviparous – produce embryos that absorb nutrients through the walls of the mother’s reproductive tract

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