Fishes – Biology Osmoregulation Chondrichthyes & Sarcopterygii Concentration of solutes in blood similar to seawater (isosmotic) or slightly higher (hyperosmotic) Retain urea and TMAO in blood (toxic to most other vertebrates) Absorb water through gills and skin Salts excreted by glomerular kidneys and rectal gland Large volumes of hypotonic urine Actinopterygii/Osteichthyes Concentration of solutes much lower than seawater (hypo-osmotic) ~14 ‰ vs. ~35 ‰ Drink seawater Salts excreted by kidneys (often aglomerular) and chloride cells in gills Small volumes of isotonic or hypertonic urine

Fig. 10-24

Fishes – Biology Buoyancy Regulation Chondrichthyes Sarcopterygii Large liver – squalene (~20% less dense than seawater) Up to 20-25% of body weight Continuous swimming Lift from broad, flat head Sarcopterygii Lipid-filled swim bladder Actinopterygii/Osteichthyes Gas-filled swim bladder Physostomes: Fill SB by gulping air Physoclists: Fill SB using gas gland (Root effect) Some fishes lack a swim bladder Active pelagic species (tunas, mackerel) Demersal or benthic species (scorpionfishes)

Fig. 10-15

Fishes – Biology Sensory Systems Smell/Taste Most fishes have a highly developed sense of smell Detect food, mates, predators, navigational information Sensory cells in olfactory sacs on both sides of head Sacs connected to outside through nares (nostrils) Sharks especially sensitive to scent of blood (1 ppm) Hammerhead sharks: nostrils on ends of “hammer”; swing head side to side; orient by comparing concentrations on left/right Salmon locate home stream by scent (imprinting) Taste with taste buds in mouth and on lips, fins, skin, barbels

Fig. 10-26

Fishes - Biology Sensory Systems Lateral line Inner ears Clusters of sensory cells (neuromasts) in small canals lining head and along sides of body Sensitive to vibrations in water Used for orientation, detection of prey and currents, avoidance of predators and obstacles Inner ears Calcareous otoliths rest on sensory hairs (maculae) Detect sound waves + changes in fish attitude Help to maintain equilibrium and balance Can be used to determine age of fish

Fig. 10-27

Fishes – Biology Sensory Systems Lateral line Inner ears Clusters of sensory cells (neuromasts) in small canals lining head and along sides of body Sensitive to vibrations in water Used for orientation, detection of prey and currents, avoidance of predators and obstacles Inner ears Calcareous otoliths rest on sensory hairs (maculae) Detect sound waves + changes in fish attitude Help to maintain equilibrium and balance Can be used to determine age of fish

Fishes – Biology Sensory Systems Electroreception Found in Chondrichthyes Ampullae of Lorenzini Detection of prey, navigation Extremely sensitive (may be less than 1 nV/cm) Can detect a marine mammal’s electric field 3 m away Used in combination with other senses

Kalmijn (1971) Spotted dogfish shark (Scyliorhinus canicula) A) Flatfish (Pleuronectes platessa) buried in sand B) Flatfish in box of agar made with seawater (blocks mechanical vibrations); flow-through C) Chopped fish in box of agar made with seawater; flow-through D) Flatfish in electrically insulated box of agar made with seawater E) Electrodes buried in sand F) Electrode buried in sand; chopped fish on surface Kalmijn (1971)

Fishes – Biology Feeding Chondrichthyes Bite pieces from large prey Tiger shark – Diverse stomach contents Great white shark – Wound and wait Cookie cutter shark – Cut out chunks Ingest smaller prey whole Nurse shark – Benthic invertebrates Filter plankton – Gill rakers Whale shark – Warm Basking shark – Cold Megamouth shark Manta ray

Fishes – Biology Feeding Actinopterygii/Osteichthyes Capture large prey whole Large mouth, small teeth Ex: Barracudas, frogfishes Crushers – Crush prey Teeth usually fused into bony plates Ex: Pufferfishes, porcupinefish, boxfishes Pickers – Ingest smaller prey whole Small mouth, tiny teeth Ex: Butterflyfishes Grazers Small mouth, strong teeth Ex: Parrotfishes, surgeonfishes Filter plankton Gill rakers Ex: Anchovies, sardines, herrings

Fishes – Biology Reproduction Modes Strategies Fig. 10-33 Oviparity Ovoviviparity Viviparity Strategies Pelagic Often in aggregations Many small eggs, high mortality Ex: Tunas, sardines, parrotfishes Benthic In pairs or aggregations Eggs usually attached or sinking Ex: Smelt, salmon Brood hiders Benthic spawners; no parental care Ex: Grunion Guarders Care of eggs until hatching, often beyond May involve territoriality Ex: Damselfishes, blennies, gobies Bearers Eggs carried by parent until hatching Care usually by males Ex: Seahorses, pipefishes, jawfish Fig. 10-33

Fishes – Biology Reproduction Hermaphroditism Larval development Synchronous Ex: Hamlets Protogyny Ex: Wrasses Protandry Ex: Anemonefishes Larval development Planktotrophic Lecithotrophic Fig. 10-34 Fig. 10-35

Fishes – Biology Schooling One form of shoaling behavior Displayed by ~25% of all fish species Some fishes school throughout life, others only when juveniles, feeding School sizes vary Atlantic herring – 4580 m3 Pacific herring – 15 miles long! Positioning in school may involve Vision Other senses (mechanical vibrations, olfaction, hearing) Types Mobile schools Usually consist of single species, size range Stationary schools May contain multiple species, sizes Functions Protection against predators Increased swimming efficiency? Beneficial when feeding Beneficial when mating

Fishes – Biology Migration Generally related to feeding and/or reproduction Diel Horizontal Ex: Grunts (day on reef, night feeding in seagrass beds) Vertical Ex: Mesopelagic fishes Large Scale Ex: Skipjack tuna feed in Eastern Pacific, spawn in Western and Central Pacific

Fishes – Biology Migration Anadromous Spawn in fresh water Spend most of life in ocean Ex: Salmon (seven species) in Pacific Ocean Spawn in shallow areas of rivers/streams Semelparous (adults die after spawning) Young migrate downstream to ocean after 0-5 years Spend 3-7 years in ocean before returning to home stream Homing behavior enabled by olfactory imprinting Important source of nutrition for wildlife, forests

Fishes – Biology Migration Catadromous Spawn in ocean Spend most of life in fresh water Ex: Eels (16 species) in Atlantic Ocean Spawn in Sargasso Sea (400-700 m or deeper) Semelparous Eggs hatch into leptocephalus larvae Larvae spend a year or more as plankton then undergo metamorphosis into juveniles Adults spend 10-15 years in fresh water before migrating to Sargasso Sea to spawn

Fig. 10-37