Genetic population structure in the Lake Tanganyika sardine Limnothrissa miodon

There was significant morphological differentiation among samples of Tangan yika sardine Limnothrissa miodon, indicating non-random association of fish . Individuals within schools appeared to be unrelated as high mtDNA haploty pe diversity demonstrated the presence of many maternal lineages in each sc hool. Nevertheless, there was evidence from allozyme analysis for genetic d ifferentiation on a very small geographical scale, possibly even among indi vidual schools, without any clear geographical boundaries among populations . Similar microgeographical differentiation at the allozyme level was found in several marine pelagic species, suggesting a general pattern of random genetic structure in pelagic schooling fish. Such genetic patchiness may ar ise from biased reproductive success in localized spawning events and long- term stability of schools, resulting in genetic differentiation among schoo ls. While the present results are preliminary, the far-reaching implication s both for fisheries management and for evolutionary processes in pelagic s pecies warrant further research on microgeographical genetic patterns using more sensitive markers. (C) 1998 The Fisheries Society of the British Isle s.