Marine Biology: Fish Biology

What are the 2 major classes of fish?

Chondrichthyes and Osteichthyes

Chrondrichthyes

-Skeletons composed of cartilage and not bone tissue

-Usually have ventral mouth with multiple rows of replaceable teeth

-5-7 pairs of gill slits

Chondrichthyes organism examples

Sharks, rays, skates, and chimera

Osteichthyes

-Rigid bony skeleton for muscular attachment

-Diverse body form with speed, habitat and feeding adaptations

-Fixed teeth on upper and lower jaws-allowing fish to chew their food

-Jaws are generally directed forward

Oviparous

How most fish reproduce meaning they shed eggs directly into the water column, or lay eggs in nests within the sediment or on substrate

How are oviparous fish eggs fertilized?

Spawning males will fertilize the floating eggs in the water column

Development of oviparous eggs

Eggs hatch and develop into yolk-sac larvae, which use the yolk for food first and zooplankton second

What type of fish makes nests for reproduction?

Garibaldi fish which lives in rocky areas. The males tend to groups of egg clusters and attract females that lay eggs in nest areas

Oviviparous

Eggs are retained by female and fertilization happens internally, but developing embryos receive no nutrition from mother during development (coelacanth)

How do fish breathe?

Water moves across the gills which extract O2 and release CO2 into the water. Oxygen rich blood is moved towards the fish by the lamella which is in gill filaments, while oxygen poor blood picks up oxygen from the water. Similar to countercurrent exchange

Does maintaining neutral buoyancy in fish significantly reduce energy cost?

Yes

Swim bladder

Used by bony fishes to adjust to bulk density by absorbing and secreting gas to adjust to the depth at which the fish is neutrally buoyant.

Do fish have muscular control of swim bladder?

No, it is driven by changes in hydrostatic pressure by changing depths

Rete mirabile

Responsible for increasing gas pressure of oxygen, allowing for gas bladder to fill in the deep sea

Gas glands of the rete mirabile

As O2 rich blood moves, they excrete lactic acid into the blood which forces hemoglobin to release oxygen so oxygen can diffuse through gland and fill swim bladder

What fish does not have a swim bladder?

Chondrichthyes (sharks, skates, rays, chimera)

Are all bony fish poikilotherms?

Yes, their body temperatures hover within 1-2 degrees of ambient water temperature

Where does homeothermy occur?

Occurs in the suborder scombroidei (tunas and mackerels, lamnidae and alopidae)

Lateral line system

Canals along each of their sides, which is a series of mechanoreceptors with separate nerves leading to brain. Respond to change in pressure in the water, helps fish to navigate and respond to threats and environmental change

Who has the lateral line system?

Elasmobranch and bony fish

Ampullae or Lorenzini

System of electroreceptors that can detect extremely small voltage from prey (bony fishes and all elasmobranchs)