A high level of genetic diversity was observed in Katsuwonus pelamis populations from India (h ¼ 0Á952, ne ¼ 14Á3) and Japan (h ¼ 0Á897, ne ¼ 8Á9). The log-likelihood (G)-based exact test revealed significant heterogeneity in the distribution of haplotypes between the two populations (P < 0Á01, S.E. ¼ 0Á001). This result suggests that the two populations should now be treated as demographically independent and managed separately. #

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Genetic structure of skipjack tuna Katsuwonus pelamis from the Indian region was investigated using sequence data of mitochondrial DNA (mtDNA) D-loop region. A total of 315 individuals were sampled from six major fishing grounds around the east and west coasts of India including the Andaman (Port Blair) and Lakshadweep (Minicoy) Islands. Nucleotide and gene diversities were high in all the sample collections. Significant genetic heterogeneity was observed for the mtDNA sequence data among sites (φ(ST) = 0·0273, P < 0·001). Analysis of molecular variance (AMOVA) showed significant genetic variation among four groups (φ(CT) = 0·0261, P < 0·05) which was also supported by spatial AMOVA results. The null hypothesis of single panmictic population of K. pelamis along the Indian coast can thus be rejected. Phylogenetic analysis of the mtDNA sequence data showed the presence of four clades of K. pelamis in the Indian waters. There was no clear pattern, however, of haplotypes and geographic location among samples. The results of this study suggest the occurrence of four genetically differentiated groups of K. pelamis across the coastal waters of India.

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Kawakawa Euthynnus affinis is an epipelagic migratory tuna species, widely distributed in the tropical and subtropical waters of the Indo-Pacific region. Kawakawa constitutes the largest tuna fishery in the Indian waters. In the present study, genetic variation was assessed using sequence analyses of Mitochondrial DNA (mtDNA) D-loop region. A 500 bp segment of D-loop region was sequenced in 400 samples collected from eight localities (Veraval (VE), Ratnagiri (RA), Kochi (KO), Kavaratti (KA), Port-Blair (PB), Tuticorin (TU), Pondicherry (PO), and Vizag (VI)) along the Indian coast. Analysis of molecular variance of mtDNA data revealed no significant genetic differentiation among sites the (U ST = 0.0028, P = 0.20723) indicating a single population along the Indian coast. Phylogenetic analysis revealed no obvious phylogeographic pattern separating the eight samples of kawakawa. However, the genealogical relationships demonstrated that mtDNA D-loop sequences belong to two different clades (clade I and clade II). Clade I is the major clade which consists of more than 98 % specimens from each regional population while clade II has individuals from only three populations (VE, PO, and VI). Results of genetic analyses of the present study support a single stock management of kawakawa along the Indian coast.

A survey of five newly developed microsatellite DNA markers in skipjack tuna Katsuwonus pelamis revealed high levels of polymorphism in two samples off the west coast of India (Minicoy Island and Kochi coast) and one sample off the Japan coast. Although significant differentiation (P < 0Á01) in the number of specific alleles was observed between Minicoy and Kochi samples, the F-statistics values among the samples were very low (average ¼ 0Á0014) and not significant (P ¼ 0Á284).

Frigate tuna Auxis thazard thazard is a cosmopolitan species and one of the smallest members of the tribe Thunnini (the true tunas), and currently managed as a single stock. In the present study, genetic variation was surveyed using sequence data of mitochondrial DNA D-loop region to test for the presence of genetic stock structure of frigate tuna along the Indian coast. A total of 364 individuals were sampled from 8 major fishing zones along the Indian coast. Significant genetic heterogeneity was observed for the sequence data (F ST = 0.0439, P = < 0.001). Analysis of molecular variance (AMOVA) showed significant genetic variation among the three groups analysed (F CT = 0.1223, P = < 0.05), which was also supported by spatial AMOVA results. Therefore, the null hypothesis of single panmictic population of frigate tuna along the Indian coast can be rejected. Phylogenetic analysis of nucleotide sequences demonstrated that frigate tuna can be grouped into three different mitochondrial clades (Clades I, II and III). However, there were no significant genealogical branches or clusters of samples corresponding to sampling locality. The results of the present study suggest the possibility of three genetically differentiated units of frigate tuna across the coastal waters of India.