Buoyancy

Specific gravity: fresh water1.0 sea water1.026 fats, oils tissues cartilage1.1 bone, scales2.0 total fish body

Strategies to deal with sinking: 1.reduce body weight - reduce heavy materials – cartilage in place of bone – deepsea fishes reduce bone and muscle Specific gravity: fresh water1.0 sea water1.026 fats, oils tissues cartilage1.1 bone, scales2.0 total fish body

Strategies to deal with sinking: 1.reduce body weight - reduce heavy materials - add lighter materials - strategy used by most sharks, a few teleosts lipids (specific gravity ~0.90) squalene (especially in the liver) ~ Mola mola uses ‘fresh’ water (lighter than sea water) Specific gravity: fresh water1.0 sea water1.026 fats, oils tissues cartilage1.1 bone, scales2.0 total fish body

Strategies to deal with sinking: 1.reduce body weight - reduce heavy materials - add lighter materials - strategy used by most sharks, a few teleosts lipids (specific gravity ~0.90) squalene (especially in the liver) ~ Mola mola uses ‘fresh’ water (lighter than sea water) using fat alone requires ~ 48% of body volume as fat (e.g., Salmoniformes – siscowet lake trout)

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) - physostomus (open to the outside) - physoclistous (sealed)

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) - physostomus (open to the outside) - physoclistous (sealed) BUT: pressure increases 1 atm for every 33’ depth (10 m)

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) - physostomus (open to the outside) - physoclistous (sealed) BUT: pressure increases 1 atm for every 33’ depth (10 m) fish do not usually change depth to bring about more than a 25% change in gas bladder volume - change from 90 to 100m decreases volume by only 10% - change from 20 to 30 m decreases by about 25%

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) - physostomus (open to the outside) - physoclistous (sealed) ~ 2/3 of all teleosts increase partial pressure of gas in blood allow passive diffusion via rete mirable

Gas bladder: lactic acid in blood circulating around bladder releases oxygen (Root effect) Cells convert glucose to lactic acid

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) - physostomus (open to the outside) - physoclistous (sealed) ~ 2/3 of all teleosts increase partial pressure of gas in blood allow passive diffusion via rete mirable deepsea fishes – higher pressures – longer capillaries gas resorbed via simple diffusion, expelled via gills

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) 3.generate lift - heterocercal tail - planing surfaces – pectoral fins, entire body Scorpaeniformes – sea moth, flying gunard Pleuronectiformes - flounder

Strategies to deal with sinking: 1.reduce body weight 2.add buoyancy compensating organ (gas bladder) 3.generate lift 4. avoid the problem – live on the bottom, use lift as needed Scorpaeniformes - sculpin

Respiration

availability of O 2 in water varies with - temperature - productivity - BOD origin of fishes in warm Tethys Sea….

Respiration lungs – lungfishes (Subclass Dipnoi – Ceratodontiformes, Lepidosireniformes) - including obligate air breathers

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars ( Polypteriformes, Lepisosteiformes, Amiiformes)

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills – most teleosts

buccopharyngeal cavity parabranchial cavity

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills - respiratory pump, or - ram ventilationram ventilation

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills modified gills - gill filaments tend to stick together in air - tough filaments handle temporary exposure to air e.g. walking catfish

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills modified gills skin - reedfish – skin supplies 32% of O 2 need despite ganoid scales - mudskipper (Periopthalmus) – 48% - eels (Anguilla) – 30-66% “eel fields”….

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills modified gills skin - reedfish – skin supplies 32% of O 2 need despite ganoid scales - mudskipper (Periopthalmus) – 48% - eels (Anguilla) – 30-66% mouth – electric eel, carp gut – Plecostomus

Respiration lungs – lungfishes modified gas bladder – bichirs, bowfin, gars “normal” gills modified gills skin - reedfish – skin supplies 32% of O 2 need despite ganoid scales - mudskipper (Periopthalmus) – 48% - eels (Anguilla) – 30-66% mouth – electric eel, carp gut – Plecostomus surface water - killifish Cyprinodontiformes

Thermoregulation

are fish “cold-blooded”? poikilotherms internal temperature varies homeotherms internal temperature remains stable ectotherms temperature is controlled externally endotherms temperature is controlled internally

thermal strategies ectotherms – thermoregulate behaviorally - switch different forms of enzymes on and off - tend to have limited thermal ranges - alter cell membrane saturated:unsaturated fat ratio to maintain fluidity

thermal strategies ectotherms – thermoregulate behaviorally - switch different forms of enzymes on and off - tend to have limited thermal ranges - alter cell membrane saturated:unsaturated fat ratio to maintain fluidity endotherms – thermoregulate physiologically - use rete mirable to conserve heat - red muscle next to spinal column to insulate heat

thermal strategies ectotherms – thermoregulate behaviorally - switch different forms of enzymes on and off - tend to have limited thermal ranges - alter cell membrane saturated:unsaturated fat ratio to maintain fluidity endotherms – thermoregulate physiologically - use rete mirable to conserve heat - red muscle next to spinal column to insulate heat thermogenesis – use of eye muscle in scombrids (mackerel) no contractile elements, many mitochondria

Extreme thermal conditions Heat: moderate - insufficient oxygen high - protein denaturation Cold: moderate - slowed molecular/biochemical reactions low - ice crystals form in tissues - solutes in remaining fluid increase concentration

Extreme thermal conditions (1) ice insulates water (2) salt water freezes at (below freezing point of tissues) (3) solutes in tissue depress freezing temp of body fluids to ~ -0.7

Extreme thermal conditions Solutions to cold: - produce antifreeze glycoproteins w. genes turned on at low temp Notothenioid kidneys lack glomeruli which would remove antifreeze glycoproteins Ice fishes Perciformes Suborder Notothenioidei

Extreme thermal conditions Solutions to cold: - produce antifreeze glycoproteins w. genes tuned on at low temps Notothenioid kidneys lack glomeruli which would remove antifreeze glycoproteins - increase concentrations of osmolytes (ions) smelt use glycerol - metabolically costly to produce (smelt known as ‘sweet fish’ in winter fishing)