1. 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

3. Fig

4. 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)

5. Fig

6. 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

7. Fig

8. 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

10. Fig

11. 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

13. 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

14. 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)

15. 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

16. 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

17. 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

18. Fishes – Biology Reproduction Hermaphroditism Larval development
Synchronous
Ex: Hamlets
Protogyny
Ex: Wrasses
Protandry
Ex: Anemonefishes
Larval development
Planktotrophic
Lecithotrophic
Fig
Fig

19. 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

20. 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

21. 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

23. 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 ( m or deeper)
Semelparous
Eggs hatch into leptocephalus larvae
Larvae spend a year or more as plankton then undergo metamorphosis into juveniles
Adults spend years in fresh water before migrating to Sargasso Sea to spawn

24. Fig