Internal Physiology of Fishes Chapter 8
Feeding • Most fishes are carnivores. • plankton feeders • demersal feeders • open water predators • Bony fishes – teeth can be found in jaw, roof of the mouth, on gill rakers, and in pharynx • Cartilaginous fishes – teeth only on jaw margin
Digestive System • mouth • pharynx • esophagus • stomach • J-shaped or elongated • intestine • anterior pyloric caeca secretes digestive enzymes • receives inputs from pancreas and liver • spiral valve • cloaca/anus
Circulatory System • Fish have a two-chambered heart. • Deoxygenated blood is pumped to the gills where gas exchange occur.
Circulation and Heat Exchange • Most fish are poikilothermic. • Few large sharks and bony fish can maintain core body temperature slightly higher than their environment. • retemirabile (‘wonderful net’) • adaptation for inhabiting colder waters
Respiratory Anatomy • Fish exchange O2 and CO2 through paired gills. • Cartilaginous fishes Bony fishes
Respiratory Anatomy – Cartilaginous vs. Bony Fishes Cartilaginous Fishes • Most swim continuously. • First pair of gill slits is modified into spiracles. • Usually 5 gill slits – may have 6 or 7. Bony Fishes • Have a single common gill chamber. • Covered by an operculum
Respiratory Anatomy • Covered by an operculum • Gill arches • Gill filaments • Lamellae • Gas exchange occurs by simple diffusion • Countercurrent system of flow
Osmoregulation • regulation of the body’s internal salt balance • Bony fish • Body fresher than seawater • Drink seawater • Salt excreted by kidney • Small amount of urine • Chloride cells • Cartilaginous fish • Rectal gland • Urea in blood • Absorb water through gills
Nervous System • Fish possess a central nervous system, consisting of a brain and spinal cord. • Variation exists. Proportional size of the lobes reflects the predominant movement and feeding behaviors of particular species. (i.e. the largest area of the lamprey brain is the cerebellum and medulla which indicates the fishes reliance on grasping with its jaw and attaching to its food).
Fish Senses • Smell – use sensory cells in olfactory sacs on both sides of the head. Each sac opens to the nostrils or nares. • During dissection, note the large portion of the forebrain devoted to smell particularly in the shark.
Fish Senses • Taste – Taste buds can be found on the mouth, fins, skin, lips, and barbels of fish.
Fish Senses • Sight – used by most fishes • Unlike terrestrial vertebrates, fish eyes focus by moving the lens closer or farther away from the subject • Shallow water species have color vision • Sharks and deeper water species may have little color vision, but see best in contrasting light situations • Some have a nictitating membrane that can cover the eye from the bottom to reduce brightness or offer protection
Fish Senses • Touch – fish possess a lateral line consisting of canals in the skin and in the bone or cartilage of the head that connect to neuromast cells that are sensitive to vibration.
Fish Senses • Hearing – perceive sound waves with their inner ears • Use fluid filled canals on either sides of the brain • Some fish amplify sounds using their swim bladder • Involved in balance – use ear stones or calcified otoliths that rest on sensory hairs
Reproduction • Sexes are usually separate. • Some fish are hermaphroditic, but usually still reproduce with other individuals. • Some fish are sequential hermaphrodites – individuals begin life as one gender and later change into the other. Sexually dimorphic sockeye salmon (male on bottom)
Simultaneous Hermaphrodites • Fish in the Salmon and Sea bass families.
Protandrous sequential hermaphroditism Initial phase: initial males and females Terminal phase: males
Fish Reproductive Anatomy • Jawless and bony fish – separate urogenital opening for urination and gamete release • Cartilaginous fish – duct leads from reproductive organ to the cloaca http://www.marinebiodiversity.ca/shark/english/skull5.htm
Reproductive behavior • Timing of reproduction controlled by sex hormones released into blood stream. • In response to maturation of gametes or to environmental cues • Potential mates come together. • Courtship • Fertilization – may be internal (most cartilaginous fish) or external (most bony fish) • Some fish tend eggs or brood nests (usually males)
Early Development • Oviparous – large number of immature eggs are laid at a single time. Larval fish hatches quickly, but still retains and absorbs yolk sac. • Ovoviviparous – female retains eggs inside her reproductive tract for protection • Intrauterine cannibalism • Viviparous – produce embryos that absorb nutrients through the walls of the mother’s reproductive tract
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