EFFECT OF SOME VERTEBRATE AND INVERTEBRATE HORMONES ON THE POPULATION-GROWTH, MICTIC FEMALE PRODUCTION, AND BODY-SIZE OF THE MARINE ROTIFERBRACHIONUS-PLICATILIS MULLER

Eight vertebrate and invertebrate hormones were screened for their eff ect on population growth, mictic female production, and body size of t he marine rotifer Brachionus plicatilis. Growth hormone (GH) or human chorionic gonadotropin (HCG) at 0.0025-25 I.U. ml(-1) and estradiol-17 beta (E-2), triiodothyronine (T-3), 20-hydroxyecdysone (20-HE), 5-hyd roxytryptamine (5-MT), gamma-aminobutyric acid (GABA) or juvenile horm one (JH) at 0.05-50 mg l(-1) were added to 5-ml of Nannochloropsis ocu lata suspension (7 x 10(6) cells ml(-1)). From an initial density of 1 individual ml(-1), rotifers were cultured with hormones for 48 hours in 22 ppt seawater at 25 degrees C, in darkness. Rotifers were counted and classified into female types and transferred to a new algal food suspension without hormone every other day until day 8 when body size was measured. Population growth was significantly higher in treatments exposed to GABA (50 mg l(-1)), GH (0.0025 and 0.025 I.U. ml(-1)), HCG (0.25 and 2.5 I.U. ml(-1)), and 5-HT (5 mg l(-1)). E-2 caused a decre ase in population growth, whereas JH, 20HE, and T-3 had no effect. Mic tic female production was significantly higher at 0.05 and 0.5 mg l(-1 ) JH and 0.05 and 5 mg l(-1) 5HT. GH (0.0025 and 0.025 I.U. ml(-1)), E -2 (50 mg l(-1)), GABA (0.5, 5 and 50 mg l(-1)), and 20-HE (0.05 mg l( -1)) treatments had significantly higher mictic female production only on day 8, 6, 4, and 6, respectively. T-3 and hCG had no effect on mic tic female production. Lorica length increased by 9.6% and 4.4% in rot ifers treated with JH (0.05 mg l(-1)) and GABA (5 mg l(-1)), respectiv ely. Correspondingly, lorica width increased by 8.9% and 2.6% in these treatments. In comparison, 20-HE-, T-3-, and HCG-treated rotifers wer e smaller (3.9-8.2%) and GH, 5-HT and E-2 had no effect on rotifer bod y size.