Role of two plasma vitellogenins from Indian major carp (Cirrhinus mrigala) in catfish (Clarias batrachus) vitellogenesis

Complete vitellogenesis (synthesis and incorporation of vitellogenin, Vg) i n the female catfish, Clarias batrachus, during different reproductive phas es (preparatory, prespawning, and postspawning) of its annual ovarian cycle is induced by administering heterologous Vg (semipurified; ULT-I and purif ied; HA-I and HA-II) isolated from the Indian major carp, mrigal (Cirrhinus mrigala). During the prespawning period, ULT-I, which contains both HA-I a nd HA-II, showed a dose-dependent response in relation to the induction of complete vitellogenesis in female catfish. In the preparatory period, daily treatment with 1 mg of ULT-I for 12 days resulted in an increase in plasma Vg level, ovarian weight, and number of stage-II (vitellogenic) oocytes al ong with the appearance of stage III (fully formed) yolky oocytes. In the p respawning period, 12-day administration of HA-I at the dose level of 0.5 m g/fish/day enhanced complete vitellogenesis in intact female catfish and in duced Vg synthesis in hypophysectomized female catfish, whereas HA-II, at t he same dose level, could only stimulate Vg synthesis, indicating their dif ferent roles during vitellogenesis. The results so far obtained may be due to the estradiol-17 beta contamination in the Vg fractions. Estimation of E -2 in ULT-I, HA-I, and HA-II by E-2 ELISA indicates that HA-II contains onl y a small amount (106 pg/mg protein). Therefore, daily treatment with 1 mg each of delipidated ULT-I and HA-I for 12 days could. synthesize very littl e Vg, whereas intact ULT-I at the same dose level induced not only a high p lasma Vg level but also increased GSI, indicating the importance of lipid i n the native molecule for the induction of vitellogenesis. During postspawn ing period, administration of HA-I (0.5 mg/fish/day for 21 days) to reprodu ctively regressed female catfish pretreated with HA-II (10 mug/fish/day for 7 days) and maintained at a long photoperiod (LD 14:10) and high temperatu re (30 degrees), induced complete vitellogenesis. (C) 2001, Academic Press.