Development of Prelarvae

Abstract

The period from hatching of the embryo to the beginning of active (exogenous) feeding is at least as long as the embryonic development. Characteristic features of this period include the replacement of embryonic adaptations and functions by the definitive ones. This change involves alterations in the relationships of the developing embryo with the environment. This affects its behavior such as response to light, substrate and water current. During this period several traits are formed, which have taxonomic value and characterize adult fish of various species: the subpharyngeal fold is formed (or not formed), differences arise in the length and location of barbels, position of the dorsal fin, structure of mouth, lower lip, and some other organs. Because of the characteristic features of this period a special prelarval period is distinguished in the development of sturgeon as in that of teleosteans (Rass 1941, 1946). This period begins with the emergence of embryos from the membranes and ends when prelarvae begin active feeding. However, until now some authors continue to refer to the prelarvae as free embryos or just as larvae, thereby ignoring fundamental differences of this developmental period both from the embryogenesis and the larval period in the strict sense of the word.