Seasonal and circadian time-dependent dual action of GH on somatic growth and ovarian development in the Asian catfish, Clarias batrachus (Linn.): role of temperature.

Effect of growth hormone (GH), injected either at the morning or evening, on the somatic and ovarian development of the Asian catfish, Clarias batrachus was studied during the late quiescence and early recrudescence phase of the reproductive cycle. GH treatment during the late quiescence phase (December-January; 11L: 13D, average water temperature 16.2+/-1 degrees C) failed to exert any impact on the somatic or ovarian development, except that it increased plasma testosterone marginally, and decreased hepatic level of triglycerides (TG); while during the early recrudescence phase (March-April; 12.4L: 11.20D; average water temperature-28.4+/-2 degrees C), GH had significant circadian time-dependent effect on somatic and ovarian development. GH injection at morning stimulated ovarian growth and development, as was evident from the dose-dependent significant increase in ovarian weight, gonadosomatic index, plasma levels of testosterone and estradiol-17beta following GH treatment. The ovarian morphology also revealed the advancement in follicular development in GH treated fish. GH also induced remarkable increase in ovarian levels of TG, free cholesterol (CF) and phospholipids (PL) with concomitant declines in their hepatic levels. However, evening hour GH injection provoked appreciable increase in body weight without having any significant impact on ovarian weight and GSI. Few oocytes in the ovary of evening hour GH treated fish exhibited advanced stages of development, but number of such advanced stage oocytes was significantly much less than the morning hour GH injected fish. Ovarian TG and PL remained unchanged, while their hepatic levels were increased. The temporal synergism between GH and other intrinsic factors regulating body growth and gonadal development may be suggested herewith to be considered prior to administration of GH in fishes. This study has immense practical use in aquaculture.