Result: The Effect of Immersion Duration of java barb larvae (Barbornymus gonionotus) in the combination of thyroxine hormone and recombinant growth hormone (rGH) on the egg yolk absorption and growth

Java barb (Tawes) is one of the endemic freshwater fish in Indonesia which has being widely cultivated. The time rearing of Java barb from larva to market size is generally 5-6 months. Egg yolk absorption rate and growth of Java barb fish can be increased by hormonal manipulation using thyroxine hormone and recombinant growth hormone (rGH). The length of immersion time affects the performance of hormones in the fish’s body. The purpose of this study is to determine the effect of immersion duration and the best immersion time in a combination of thyroxine and rGH on the egg yolk absorption and the growth of Java barb larvae. This research was conducted on 23 August-1 November 2021 at Laboratorium Pengujian Kesehatan Ikan dan Lingkungan (LPKIL) in Muntilan, Magelang regency. The testing fishes used were early hatched Java barb fish larvae that still had egg yolks. The method used was a completely random design (CRD) with 4 treatments and 3 replications and each was done with a combination of 0.1 mg/l thyroxine hormone and 2.5 mg/l rGH with treatments A (control), B (1 hour immersion time), C (2 hours immersion time) and D (3 hours immersion time). The results showed that the effect of immersion duration in combination of thyroxine and rGH had a significant effect on the rate of egg yolk absorption and the growth of Java barb fish larvae. The best immersion time was treatment D (3 hours immersion duration) which resulted in 4%/hour of the absorption rate of egg yolk absorption rate, 12.53±0.15 mm absolute length growth, 0.047±0.002 g absolute weight growth, 13.82±0.15 % of specific growth rate, and 54.67±4.62 % survival rate.