Estimation of Genetic Variation through Isozyme Analysis in Freshwater Sardines, Sardinella tawilis (Herre), from Two Portions of Taal Lake: Agoncillo and Talisay, Batangas

Genetic variation in freshwater sardines, Sardinella tawilis (Herre), from two portions of Taal Lake (Agoncillo and Talisay, Batangas in the Philippines) was determined through isozyme analysis using four enzyme systems: acid phosphatase (ACP), alkaline phosphatase (ALP), esterase (EST), and malic enzyme (ME). The degree of genetic variability within subpopulation and between subpopulations was determined by calculating several genetic measures, particularly the proportion of polymorphic loci (P), average number of alleles (A), average heterozygosity (H), genetic identity (I-N), genotypic similarity (I-H), genetic distance (D), and by applying Wright's F statistic (F-ST). Results revealed four presumptive loci in both subpopulations (ACP-1, ALP-1, EST-1, and ME-1). Among organs, the heart showed the highest genetic variation based on the P (0.75), A (1.75), and H (0.369-0.371) values in both subpopulations. The computed I-N, I-H, and D showed the same trend in the two subpopulations where eye tissues had greater relatedness with muscle tissues. Although both subpopulations have the same trend, a higher genetic variation was seen in the organs of the Agoncillo subpopulation than in the organs of the Talisay subpopulation as indicated by their F-ST values, 0.321 and 0.162, respectively. The two subpopulations, when compared, revealed the same values for P (0.75) and A (1.75). However, average heterozygosity was slightly higher in the Talisay subpopulation (H = 0.291) than in the Agoncillo subpopulation (H = 0.249). The computed values for I-N, I-H, and D implied a high relatedness between the two subpopulations. This result was further supported by their F-ST value of -0.015 which indicated low genetic variation.