Microsatellite marker-based variation in the growth hormone genes of Nile tilapia (Oreochromis niloticus)

Abstract

Polymorphisms in growth hormone genes have been found to cause variation in growth performance of fish. The objective of the study was to reveal variations in microsatellite loci located in the growth hormone genes of Nile tilapia (Oreochromis niloticus). Five microsatellite loci namely GH-MS01, IGFII, IGFII-MS01, IGFII-MS03, and STR were analyzed to assess the genetic variation in the growth hormone genes of four stocks of O. niloticus viz. FBG-Mini Hatchery, FM-Mini hatchery, Eon Aquaculture Ltd. and BFRI. The microsatellite markers were amplified by polymerase chain reaction, separated by polyacrylamide gel electrophoresis and visualized through ethidium bromide staining. All the five loci were found to be polymorphic. The average number of alleles of FM-Mini hatchery stock (3.8) was found to be highest and that of the FBG-Mini hatchery (2.8) and Eon Aquaculture stocks was found to be lowest. The average observed heterozygosity (H_o) value of the FM-Mini hatchery stock was the highest (0.140) and that of FBG-Mini hatchery stock was the lowest (0.040). On the other hand, the average expected heterozygosity (H_e) was highest in the BFRI stock (0.660) and lowest in the FM-Mini hatchery and FBG-Mini hatchery stock (0.432). The fixation index (1 - (H_o / H_e) values were positive in all the loci (except locus GH-MS01 in Eon Aquaculture stock), which means these stocks (O. niloticus) were deficient in heterozygosity. Deviation from Hardy-Weinberg expectation at STR locus in FBG-Mini hatchery and Eon Aquaculture stocks were not significant but in all other cases the deviations were found to be significant. The results provide evidence that genetic variation exists within the growth hormone genes in all four stocks of O. niloticus. The polymorphisms that have been detected in the present study can be used to study association with growth and thus selection of fast growing Nile tilapia in Bangladesh.