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Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in the esophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches called pyloric caeca, which secrete digestive enzymes and absorb nutrients.
A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits.Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians.
Cartilaginous fish produce a small number of large yolky eggs. Some species are ovoviviparous, having the young develop internally, but others are oviparous and the larvae develop externally in egg cases. [4] The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish.
The thickening is referred to as the germ ring and is made up of a superficial layer, the epiblast which will become ectoderm, and an inner layer called the hypoblast which will become endoderm and mesoderm. [6] As the blastoderm cells undergo epiboly around the yolk the internalization of cells at the blastoderm margin start to form hypoblast ...
Some non-Antarctic species either produce no or very little antifreeze, and antifreeze concentrations in some species are very low in young, larval fish. [3] They also possess aglomerular kidneys, an adaptation that aids the retention of these antifreeze proteins.
Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals. [2] [3] Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about 1 millimetre (0.039 in).
As medusae, they eat a variety of crustaceans and fish, which they capture using stinging cells called nematocysts. The nematocysts are located throughout the tentacles that radiate downward from the edge of the umbrella dome, and also cover the four or eight oral arms that hang down from the central mouth.
Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.039 in). The eggs are generally surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish have thick, leathery coats, especially if ...