I. I.Fishes – Biology E. E.Osmoregulation 1. 1.Chondrichthyes & Sarcopterygii Concentration of solutes in blood similar to seawater (isosmotic) or slightly.

I. Fishes – Biology

E. Osmoregulation1. 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

2. 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

I. Fishes – Biology

F. Buoyancy Regulation1. Chondrichthyes

• Large liver – squalene (~20% less dense than seawater)• Up to 20-25% of body weight

• Continuous swimming• Lift from broad, flat head

2. Sarcopterygii• Lipid-filled swim bladder

3. 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

I. Fishes – Biology

G. Sensory Systems1. 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

I. Fishes - Biology

G. Sensory Systems2. Lateral line

• 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

3. 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

I. Fishes – Biology

G. Sensory Systems2. Lateral line

• 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

3. 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

I. Fishes – Biology

G. Sensory Systems4. 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)

A) Flatfish (Pleuronectes platessa) buried in sand

B) Flatfish in box of agar made with seawater (blocks mechanical vibrations); flow-through

Spotted dogfish shark (Scyliorhinus canicula)

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

I. Fishes – Biology

H. Feeding1. Chondrichthyes

a. Bite pieces from large prey• Tiger shark – Diverse stomach contents• Great white shark – Wound and wait• Cookie cutter shark – Cut out chunks

b. Ingest smaller prey whole• Nurse shark – Benthic invertebrates

c. Filter plankton – Gill rakers• Whale shark – Warm• Basking shark – Cold• Megamouth shark• Manta ray

I. Fishes – Biology

H. Feeding2. Actinopterygii/Osteichthyes

a. Capture large prey whole• Large mouth, small teeth• Ex: Barracudas, frogfishes

b. Crushers – Crush prey• Teeth usually fused into bony plates• Ex: Pufferfishes, porcupinefish, boxfishes

c. Pickers – Ingest smaller prey whole• Small mouth, tiny teeth• Ex: Butterflyfishes

d. Grazers• Small mouth, strong teeth• Ex: Parrotfishes, surgeonfishes

e. Filter plankton • Gill rakers• Ex: Anchovies, sardines, herrings

I. Fishes – Biology

I. Reproduction1. Modes

a. Oviparityb. Ovoviviparityc. Viviparity

2. Strategiesa. Pelagic

• Often in aggregations• Many small eggs, high mortality• Ex: Tunas, sardines, parrotfishes

b. Benthic• In pairs or aggregations• Eggs usually attached or sinking• Ex: Smelt, salmon

c. Brood hiders• Benthic spawners; no parental care• Ex: Grunion

d. Guarders• Care of eggs until hatching, often beyond• May involve territoriality• Ex: Damselfishes, blennies, gobies

e. Bearers• Eggs carried by parent until hatching• Care usually by males• Ex: Seahorses, pipefishes, jawfish

Fig. 10-33

I. Fishes – Biology

I. Reproduction3. Hermaphroditism

a. Synchronous• Ex: Hamlets

b. Protogyny• Ex: Wrasses

c. Protandry• Ex: Anemonefishes

4. Larval developmenta. Planktotrophic

b. Lecithotrophic

Fig. 10-35

Fig. 10-34

I. Fishes – Biology

J. 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)

1. Typesa. Mobile schools

• Usually consist of single species, size rangeb. Stationary schools

• May contain multiple species, sizes2. Functions

a. Protection against predatorsb. Increased swimming efficiency?c. Beneficial when feedingd. Beneficial when mating

I. Fishes – Biology

K. 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

I. Fishes – Biology

K. Migration1. 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

I. Fishes – Biology

K. Migration2. 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