Stock structure of sea lamprey (Petromyzon marinus, L.) in Portugal exposed by fatty acid signature

Abstract

European populations of sea lamprey have declined dramatically over the last 30 years and several authors have pointed out a reduction in sea lamprey population abundance also in Portuguese rivers, which led to the fact that the sea lamprey it is classified in the Red List of Threatened Species as “vulnerable” (Rogado et al., 2005a). Marr (1957), defined the stock as a population or portion of a population which all members are characterized by similarities which are not heritable, but are induced by the environment and which include members of several different subpopulation. The spawning areas are normally clearly distinguished among the different stocks, but since fish may undertake considerable migrations, catches may also consist of fish from several stocks. Recent reports have suggested that fatty acid composition of phospholipids in some body tissues (e.g., heart tissue, brain, eggs) have a stable genetics basis, make these tissues appropriate as stock identifiers. In this context, the purpose of this investigation was thus to analyze the stock structure of Petromyzon marinus sampled in Portuguese river basins by the use of heart tissue fatty acid signature. Adult sea lampreys were collected near the river mouth of eight Portuguese river basins (i.e. Minho, Lima, Cávado, Douro, Vouga, Mondego, Tagus and Guadiana) at the beginning of their spawning migration. Heart total lipid extraction was obtained by accelerated solvent extraction (ASE) and FAME were prepared by transesterification with methanol-boron trifluoride and analysed by GC. FAMEs were identified by comparison of their retention times with known standards chromatographed in identical gas chromatography conditions. The fatty acid profile of the heart tissue varied among individuals of the different river basins. A Multiple Discriminant Analysis (MDA) was employed to identify which fatty acid contributed most to these differences. The MDA proved to be statistically significant and the overall corrected classification rate estimated from cross-validation procedure was 86.2%. Although in Tagus and Guadiana most of the individuals were correctly classified (100% and 94.7%, respectively), there are a few individuals of the other 5 watersheds that have profiles identical to those observed in these two river basins. The results are discussed in terms of fatty acid origin and hypothesis concerning the migratory behavior that could lead to these results. The fatty acid profile of heart is considered more stable than other organs, but it still exhibits some variability. This study seems to point out the potential for fatty acid compositions to discriminate sea lampreys from Portuguese river basins. Detected differences are probably related with environmental variables that they may have been exposed during early stages of their life cycle.