APBI 419 - Anatomy + Physiology

Fins

• anatomical features on body of fish and provide stability in the water

  • supported by skeleton of fish

  • are either paired or unpaired

    • paired = pectoral + pelvis

    • unpaired = dorsal, caudal, adipose, anal

  • rays on either can be soft + flexible or modified into spines to strengthen fins

Dorsal fin

• mainsail along back of fish between tail fin and head; provides stability so fish can swim in straight line

  • can't swim --> won't live long --> can't compete for food or evade predators

 

• some tropical fish have a doubled dorsal fin; part of it is a spine that resembles a straight razor and can inflict puncture wounds while second part is a stabilizer

  • used to intimidate + threaten

  • can also use an erect and locked fin as a wedge to jam into tight areas of coral so predator can't pull it out

Caudal fins

•  tail fin; sudden forward movements and for fast swimming patterns

  • also used to slow forward movement and to help make turns

  • can lengthen the fin through artificial selection → produced slower moving fish for aquariums → wouldn't survive long in wild

Anal fin

on the underside of fish between pelvic and caudal fins; provides stability, keeps fish from rolling over and going belly up

• in some species, male's anal fin acts as sexual organ and is known as gonopodium

some characins develop breeding tubercles / small hooks that're on the fins of males and not specifically for attaching to mates

Pectoral fins

•  stability as fish moves through water, hovers, and makes slow turns; near bottom of fish beneath gill openings

  • used for navigation and always in motion

  • many tropical species use them during incubation of eggs, fanning eggs w/ water during brooding period

Pelvic fins

• homologous to legs and are supported by pelvic girdle; stabilizers

  • might be highly modified like in freshwater angelfishes and gouramis so they're threadlike

  • some might use them as "feelers" to sense surroundings

Adipose fin

• few tropical fish species and most of aquaculture-reared fish (salmonids) have extra fin located on back between dorsal and tail

  • these contain mechanosensory and proprioceptive functions

  • helps detect water flow and might help with swimming performance

Lateral line

• on both sides of body and runs from back of eye to base of tail fin

  • made of small neuromasts that contain cilia in fluid-filled canals + superficial (surface-level) neuromasts

  • detects vibrations in water (low freq pressure waves)

  • fish feel → forms mental map for them; like hydrodynamic map / mechanosensory field

Skin

•  first barrier to environment; maintains osmotic integrity of fish

  • freshwater: osmotic challenge is water flooding IN (hypoosmotic environment) so fish has to expel excess water and retain ions

  • marine: vice versa, they lose water to the hyperosmotic environment

2 main layers:

1. outer epidermis overlaid by v delicate clear covering of secreted material that lays over the scales (the mucus layer)

2. inner dermis

Mucus

• protective and forms slimy outer covering of fish

  • can get small particles of material that can irritate fish (parasites, bacteria, heavy metal salts that're sloughed off)

  • increases when fish becomes stressed

Dermal skeleton

• various types of scales / plates that develop early in life (fry stage)

• salmonids: cycloid scales

• once fish has all scales no more develop as it grows

  • scales will grow and become larger w/ the fish

• not all fish have scales (catfish + eels)

Gills

• vascularized structures (blood moving systems) contained in chambers located on both sides of head region

  • water is continually passed over

    • imp site for excretion of nitrogenous wastes

Operculum

• bony flap; gill cover that protects gill structures

  • 4 cartilaginous branchial arches in each chamber that have forward facing cartilaginous projections called gill rakers

vary in morphology

• long and thin, short and knobby

species and diet dependent

Gill rakers

• help filter feeding fish trap food particles from the water and help piscivorous species prevent escape of prey through gill slits

  • tend to vary in #, length, spacing based on diet

  • gill arches support gill filaments that're directed away from mouth opening

Lamellae

• Gill filaments further subdivided into feather like structure

• these contain fine, flattened capillaries and are thinly covered by cells

  • primary lamellae = actual gill filaments

  • secondary lamellae = extend perpendicular from/are arranged on primary lamellae

    • essential in respiration / breathing of fish and are location where gas exchange occurs

Branchial pump

• how water is passed through gills

  • water drawn into mouth as opercula closes → expelled across gills 60-80% (peak efficiency = 85%) O2 extracted by secondary lamellae

  • oxygen depleted water discarded

Pseudobranch

inner side of gill cover on salmonids

• receives oxygenated blood only; doesn't function in respiratory gas exchange

  • might secrete O2 to retina of eye but still confusion as to exact function

 

Striated/skeletal muscle

• major portion of fish muscle

  • white muscles - fast-twitch, anaerobic muscle for burst swimming (bulk of myotomes)

  • red muscle - slow-twitch aerobic muscle tissue for sustained swimming; typically found as thin lateral strip along body often near lateral line

• arranged in symmetrical fashion down each side of body in series of similar segments (myotomes) that're attached to flexible spine

  • segments prominent at surface of skinned or sectioned fish

  • divided by lateral line into upper and lower sections in salmonids

Axillary muscles

muscles at base of pectoral fins

Digestive system

• degrades large particles of food into smaller components that're able to absorb across intestinal wall and into circulatory system for transport to cells of body

  • cells utilize nutrients brought by blood as building blocks for number of functions (maintenance of existing tissues, growth of new tissue, source of energy for locomotion and metabolic processes, components of body fluids, production of enzymes and hormones)

• modified according to feeding habits and food material they consume aka ecologically diverse habitats

  • carnivorous fishes: short gut + herbivorous fishes have long digestive tracts

Pylorus

constriction of digestive trat that acts as boundary between stomach and intestine

• one way valve preventing passage of large food particles

Pyloric caeca

• finger like structures extending from intestine; vary in size and number depending on species

  • have digestive and absorptive functions and usually surrounded by adipose tissue

 

Pancreas

• makes digestive enzymes and is found between pyloric caeca in salmon

  • is diffuse in salmonids (scattered among pyloric caeca and mesentery)

  • involved in many viral infections: IPN, IHN, VHS

  • also site for other bacteremias and some parasites

 

• contained in pyloric caeca structure scattered throughout fatty tissue

• it secretes digestive enzymes through pancreatic duct into intestine and secretes hormones into bloodstream

• v significant in viral disease because it's a common site for multiplication of several viral agents associated w/ fish disease

 

Liver

•  large organ located in front of stomach

  • pinkish-brown in colour, soft, and easily ruptured

  • acts as accessory digestive organ

  • involved in detoxifying the system

  • secretes bile through duct into gall bladder (small greenish sac)which temporarily stores bile

  • has secondary duct leading from gall bladder and discharges bile into anterior intestine past pylorus → breakdown of fat

abnormalities: buildup of unhealthy fats → increase in liver size + parasite invasion

pale, enlarged, whitish nodules → health problem

Swim bladder

• organ responsible for maintaining hydrostatic (pressure) equil within environment

  • depending on hydrostatic pressure at any depth in water column, gas bladder fills / secretes gas to maintain fish at desired depth w/ minimum expenditure of energy