Stream production, fish dispersal and genetic variation

Posted on December 15, 2011

Advances in molecular genetics mean that it is possible to map the family relationships of individual animals on the basis of tissue samples collected in the field.  Together with mark-recapture and radio-tracking techniques, genetic analyses can clarify patterns of dispersal by fish and other aquatic fauna.  Movements of brown trout (Salmo trutta) in a stream in the Spanish Pyrenees have been reconstructed by carrying out microsatellite analysis on DNA extracted from the adipose fins of 140 fish.  Young individuals (those less than two years old) from the same family tended to occur in the same vicinity, suggesting that dispersal from the nursery areas was limited.  However, for older fish genetic differentiation between locations was low and there was evidence for dispersal over distances of several kilometres.  Interestingly, the strong dispersal of Spanish trout contrasts with the behaviour of the same species in northernEurope, where fish were found to be more sedentary and clustering of related older individuals was recorded.  The fact that Spanish trout dispersed actively and had relatively small family and population sizes could have been a result of low stream productivity and the need for fish to move further in search of foraging sites.  One applied recommendation to emerge from this study is that population sampling should not be limited to short stretches of stream, to ensure that enough families are represented to capture the full range of genetic variation in the population as a whole. 

Reference:  Vera, M., Sanz, N., Hansen, M.M., Almodovar, A., Garcia-Marin, J.L.  2010.  Population and family structure of brown trout, Salmo trutta, in a Mediterranean stream.   Marine and Freshwater Research, 61, 672–681.