Muhammad Zairin Junior

Genetic Diversity of Boeseman's Rainbowfish (Melanotaenia Boesemani) Reared in Indonesian Farms Compared to Endangered Natural Populations

Endemic to two lakes (Ayamaru and Uter) of West Papua (Indonesia), the Boesemans Rainbowfish Melanotaenia boesemani Allen & Cross, 1980 is a very popular ornamental freshwater fish. As a result, this rainbowfish species faces great threats and is on the red list of endangered species. Therefore, rearing of this species in aquaculture systems appears to be a promising solution to limit capture of wild specimens and prevent its extinction. Although its reproduction cycle has been controlled for more than 30 years, very few farms still raise M. boesmani, probably due to the problems reported by the farmers, such as decline of production, higher proportion of females per spawning, loss of coloration, lower growth rate and fecundity. Using 12 microsatellites previously developed for this species, comparison of genotypes within six farms around Jakarta indicated that all reared strains originated from Ayamaru Lake. No deficit in heterozygotes was evidenced, suggesting that there was no major inbreeding in these reared populations. Genotype analysis also suggested that M. boesemani species is a metapopulation composed of genetically differentiated populations. Altogether, these results indicate that the problems experienced by the farmers are due not to inbreeding depression but to other factors such as inadequate management and/or poor water quality. Yet, increasing aquaculture production is probably the most effective way to alleviate the pressure that M. boesemani faces in its natural environment.

Aromatase gene expression and masculinization of Nile tilapia immersed in water 36 °C containing 17α-methyltestosterone

ABSTRACT Immersion of undifferentiated larval tilapia in high temperature and 17α-methyltestosterone (MT) cab increase the male ratio. However, the effectiveness of immersion in high temperature of water containing MT remains to be evaluated. The purposes of this study were: 1) evaluate the male ratio, growth, and survival of tilapia, and 2) analyze the aromatase brain-type gene expression level in tilapia after immersing in high temperature (36 °C) containing MT at 2 mg/L for four hour with single and double immersion. Aromatase gene expression was analyzed by semi-quantitative RT-PCR (sqRT-PCR) method. The result showed that higher monosex male ratio was obtained by single immersion of MT at 36 °C at room temperature. Gene expression level of aromatase brain-type was lower on single immersion and increased significantly at second immersion compared to control (immersion at room temperature without MT). Immersion using MT and high temperature had no significant effect on fish survival. However the specific growth rate and fish biomass were higher than control. Thus, monosex male tilapia can be produced by single immersion of undifferentiated larvae at 36 °C temperature containing MT. Keywords: male ratio, aromatase, Oreochromis niloticus , temperature, 17α-methyltestosterone ABSTRAK Perendaman larva ikan nila yang belum terdeferensiasi kelaminnya dengan suhu tinggi dan hormon 17α-metiltestosteron (MT) dapat meningkatkan nisbah kelamin jantan. Tetapi, efektivitas perendaman menggunakan MT pada suhu tinggi belum diteliti. Tujuan dari penelitian ini adalah 1) mengevaluasi nisbah kelamin jantan, pertumbuhan, dan kelangsungan hidup ikan nila, dan 2) menganalisis ekspresi gen aromatase tipe-otak pada ikan direndam menggunakan MT dengan dosis 2 mg/L selama empat jam sebanyak satu dan dua kali perendaman pada suhu 36 °C. Ekspresi gen aromatase dianalisis menggunakan metode RT-PCR semi-kuantitatif (sqRT-PCR). Hasil penelitian menunjukkan bahwa kombinasi perendaman MT satu kali pada suhu 36 °C lebih tinggi menghasilkan ikan nila jantan monoseks dibandingkan perendaman MT satu kali pada suhu ruang. Tingkat ekspresi gen aromatase tipe otak pada perendaman satu kali lebih rendah, dan meningkat secara signifikan pada perendaman kedua dibandingkan dengan kontrol (perendaman pada suhu ruang tanpa MT). Perendaman larva menggunakan MT dan suhu 36 °C tidak berpengaruh nyata terhadap kelangsungan hidup, tetapi laju pertumbuhan spesifik dan biomassa ikan perlakuan tersebut lebih tinggi daripada kontrol. Dengan demikian, ikan nila jantan monoseks dapat diproduksi dengan perendaman satu kali pada larva yang belum terdeferensiasi jenis kelaminnya menggunakan MT pada suhu 36 °C. Kata kunci: rasio jantan, aromatase, Oreochromis niloticus , suhu, 17α-metiltestosteron