Histological indices of the nutritional condition of sardine, Sardina pilchardus (Walbaum) larvae off the north coast of Spain

Larvae of sardine (Sardina pilchardus) were sampled off the north coast of Spain from March to June 1992 as part of a programme to investigate factors affecting subsequent recruitment. Histological analyses of the larvae were carried out as a measure of nutritional condition for comparison with environmental variables and subsequent survival at the juvenile stage. Tissues were grouped into short-term indicators of nutritional condition, including the digestive tract, liver and pancreas, and long-term indicators represented by cartilage, notochord and muscle tissue. Long-term indices showed little difference between months, most specimens being in relatively good condition. Short-term indices showed greater variation because larvae sampled in March and May were in significantly poorer condition than those in April and June. A third measure of condition, the presence of irreversibly damaged tissue indicated that larvae sampled in March were in the poorest condition. This measure of condition was suggested as being the most objective assessment with respect to potential larval mortality. It was not possible to compare larval condition with survival to the juvenile stage because only an insignificant number of larvae from spawning along the north coast of Spain recruited to the nursery area; most juveniles were derived from spawning further to the south. It was suggested that offshore transport associated with upwelling off the north-west coast was responsible for the loss of larvae from the north coast and may be a more significant factor in determining recruitment than nutritional condition. (C) 1997 Elsevier Science B.V.