Abstract
Fisheries management continues to be a nightmare due to over exploitation of fish stocks and various anthropogenic activities resulting in a reduction of genetic resources. Opsaridium microlepis, a commercially exploited fish species from Lake Malawi, is no exception, hence it is listed among as endangered species. Opsaridium microlepis stocks from four different rivers, were analyzed using 13 geometric morphometric landmarks and 20 microsatellite loci, to determine if the stocks were morphologically and/or genetically different. AMOVA performed on DNA data revealed a significant (P < 0.001) genetic differentiation with 16.4% of the total genetic variance ascribed to differences among populations, and 83.6% due to differences within population. This finding was supported by higher pairwise FST values (FST = 0.17). MANOVA of morphological data showed significant body shape variation among the stocks (Wilk’s λ = 0.0913; P < 0.0001). Pairwise comparisons using both methods indicated that all pairs were significantly different, except morphologically for Bua and Linthipe (P=0.3311). The morphological differences observed consisted of shorter gape and shorter head were thatof the Bua/Linthipe stock was seen in the North Rukuru and Dwangwa stocks. The morpho-genetic differentiation revealed in this study implies that the populations are distinct and should be considered as separate management and conservation units. Key words: Lake Malawi, Mpasa, procrustes distance, genetic differentiation, endangered species, fish stocks, conservation.
Highlights
Lake Malawi, a global biodiversity asset, has attracted worldwide attention amongst evolutionary biologists, due to the fastest large-scale adaptive radiation ever recorded in evolutionary history (Ribbink, 2001)
AMOVA revealed a significant (P < 0.001) genetic variation with 16.4% of the total genetic variance attributed to differences among populations and 83.6% was due to differences within population
Geometric morphometrics as used in this study has proved more robust than the traditional morphometric approach which could not clearly distinguish these stocks according to Chigamba et al (2012)
Summary
Lake Malawi, a global biodiversity asset, has attracted worldwide attention amongst evolutionary biologists, due to the fastest large-scale adaptive radiation ever recorded in evolutionary history (Ribbink, 2001). It has been known that catches have been on the decline (Tweddle, 1981; GoM, 2016) During their spawning migrations, Mpasa are heavily exploited by gillnets set near river mouths, and numerous fishing methods in the rivers themselves. Mpasa is known to inhabit the Lake Malawi and its in-flows, it has disappeared in some inflows where it used to be abundant due to ecosystem degradation, overfishing during migration (Ndamala, 2006), and a surge in human population density in the areas surrounding the in-flow rivers (Kingdon et al, 1999). Management procedures must be put in place in order to conserve the species; such management procedures require information on whether different affluent rivers inhabit different stocks or one panmictic population in the lake whose individual fish are free to go up into any river. This study aimed at unraveling whether stocks from different rivers were morphologically and/or genetically similar or not, since such information is crucial in the management of stocks/species
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