The relevance of mitochondrial lineages of Taiwanese cultured grey mullet, Mugil cephalus, to commercial products of Roe

Abstract

Mugil cephalus is an important aquaculture species in Taiwan with highly valuable roe. In order to obtain its roe, mullet fry from various Taiwan estuaries are raised in aquaculture ponds until maturity. However, not all female mullets have developed ovaries. Therefore, we have attempted to use DNA profiling to aid selection of mullet fry for aquaculture. A large proportion of North coast mullet and some West coast mullet were identified as cytochrome oxidase subunit I (COI) mitochondrial lineage 1. COI mitochondrial lineage 2 was dominant in the west and east coast estuaries, whereas COI mitochondrial lineage 3 was fewest and only was present in Chang-hua county (middle west of Taiwan). The gonadosomatic index (GSI) of lineage 1 individuals ranged from 0 to 5, no matter where the mullet fry were captured. The GSI of both the west and east coast lineage 2 individuals ranged from 0 to over 15, but the GSI of lineage 2 of the I-lan (north east of Taiwan) population was generally lower than that of western populations. These findings suggest that a genetic difference whereby west coast lineage 2 mullet yield heavier roe although the body size of lineage 1 individual is larger than that of lineage 2. Thus, lineage 2 individuals with their normal GSI distribution are the most economically viable. The application of the rapid screening of mitochondrial lineages is expected to help aquaculture farmers cultivate lineage 2 fry for roe production rather than lineage 1.