Lesson 10: Biological Features Flashcards
Do fish have transparent or non-transparent chorion?
Transparent
Integument in fish?
They do not have a keratin layer over the epidermis. Scales are dermal plates covered with epidermis. Elasmobranchs have placoid scales which give them a sandpaper texture. Although teleost fish may also have ctenoid scales, teleosts usually feel smooth to the touch, because they have cycloid scales and are often protected by a mucus layer. Fish with cycloid scales may be aged by the concentric ring pattern of their scales.
Respiratory?
The main organ of gas exchange in fish is the gills, which are found on both sides of the head. The gills contain gill filaments, feather-like structures laid out in rows that provide a large respiratory surface, which serve to keep the fish’s blood oxygenated. Bony fish have an operculum that covers their gills. When water enters the bony fish’s mouth, the jaw and operculum pump the water through the gills. Dissolved oxygen is exchanged from the water to the blood in these gill filaments. Simultaneously, waste carbon dioxide is exchanged from the blood to the water as the water is pumped over the filaments and exits behind the operculum.
Digestive?
With the exception that the intestines of fish cannot be divided into small and large intestines; the digestive tract of fish is comparable to that of mammals.21 There may be additional, species-specific modifications, such as the lack of a true acid stomach in cyprinids (including zebrafish), the presence or absence of pyloric caeca, and other differences in teleosts vs. elasmobranchs.
Buoyancy?
The swim bladder is a gas-filled sac, which is dorsal to the gastrointestinal tract and developed as an extension of the gut. It gives the fish buoyancy so they can maintain their vertical position in the water without having to swim forward. Fish can adjust their position in the water column by controlling the amount of air in the swim bladder. Fish lacking a swim bladder, such as the shark, must continuously swim, rest on the bottom of the sea, or rely on other mechanisms (such as a very large liver in sharks) to aid in regulating buoyancy.
Excretory?
Like most other aquatic animals, fish excrete ammonia. The gills release nitrogenous waste into the water. The kidneys function to excrete wastes and help the fish manage their ammonia levels. Water tends to leave the bodies of saltwater fish through osmosis. Saltwater fish drink copious amounts of seawater as part of this process. Consequently, their kidneys concentrate waste and try to put as much water back into the body as possible. The opposite is true for freshwater fish; they are constantly taking on water. Their kidneys work to rid the body of huge volumes of dilute urine. A few species of fish have kidneys that function in either freshwater or saltwater.
Endocrine?
The endocrine system of fish differs from other animals because most fish do not have a true adrenal gland. Fish have inter-renal cells near the kidney, which secrete glucocorticoids and mineralocorticoids. In general, fish have endocrine tissues or glands that are comparable in function to the mammalian endocrine system; however, their location and arrangement may be quite different.
Circulatory?
Fish have a two-chambered heart consisting of one atrium and one ventricle. The sinus venosus and bulbus arteriosus are sometimes referred to as the third and fourth chambers, respectively. The ventral aorta and arterial branches carry blood from the heart to the gills to become oxygenated. The oxygenated blood is then returned to the dorsal artery and pumped to the rest of the body.
Hematopoietic/Reticuloendothelial?
Fish lack lymph nodes, but they do have a thymus. Phagocytic cells, including macrophages, are present throughout the fish’s body (including in the pigmented macrophage aggregates). The liver, kidney, and spleen contain melanomacrophage centers, which increase in number under stress. Fish do not have bone marrow. The spleen and kidneys produce blood cells (white and red). The red blood cells are elliptical in shape and nucleated.
Reproduction?
Most fish are oviparous (eggs develop outside of the mother’s body). In most cases, fertilization is external as the sperm and the egg are expelled into the water. After the egg is fertilized, the resulting embryo receives nutrition from the egg yolk while it develops. Sometime later, the embryo hatches and is then referred to as a larva (plural: larvae). Larvae differ significantly in appearance from juvenile and adult fish.
Nervous?
With the exception of sharks and a few other species, fish generally have a much smaller brain mass than comparably sized mammals. The sense organs of fish are well developed. Some species of fish have color vision comparable to humans. Chemoreceptors found in some fish provide a highly developed sense of smell and taste. Fish have internal ears, but their sense of hearing generally is not well developed. Like amphibians, most fish have a lateral line system. The lateral lines may appear as faint lines that run from near the gills to the tail down both sides of the body. The lines contain sensitive receptors that detect vibration and movement and allow the fish to orient themselves in the water.
