GUT ANALYSIS OF FIRST-FEEDING ANCHOVY LARVAE FROM THE PATAGONIAN SPAWNING AREAS IN RELATION TO FOOD AVAILABILITY

Gut contents of Engraulis anchoita first-feeding larvae from the three Patagonian spawning areas were analysed, and related to food availabi lity and hydrological structure of the tidal front occurring in the re gion. Potential microzooplanktonic prey was homogeneously distributed in mixed water and aggregated above the thermocline of stratified shel f waters. Nauplii and eggs of copepods were the most abundant organism s, mostly ranging between 45 and 90 mu m in width. Day-night distribut ion of microzooplankton did not show evidence of diel migration. After dissection of larval guts, contents were stained with tolouidine blue , and type, size and number of food particles determinated. A nyctemer al rhythm of feeding was clearly observed, with a maximum between 8 h and 20 h, decreasing sharply at night. Feeding incidence was lowest in the nearshore mixed waters increasing progressively in stratified she lf waters. The same trend was observed for the number of prey per larv a. Nauplii of small copepods Paracalanus parvus, Oithona spp., Acartia tonsa, Microsetella norvegica and Euterpina acutifrons constituted th e bulk of ingested food of anchovy larvae followed by copepod eggs. Ti ntinnids were an important prey only in transitional waters. Dinoflage llates,lamellibranch larvae, pollen grains, spores of plants and diato ms were only occasionally found. 62% of prey analyzed had widths rangi ng from 45 to 90 mu m. Results from larval gut analysis were related t o microzooplankton distribution in different hydrographic conditions. Evidence of selectivity on nauplii were observed in all cases. On the basis of the prey distribution and larval feeding activity, it is sugg ested that transitional and stratified sectors of the patagonian front al systems could provide better feeding conditions for survival and gr owth of early anchovy larvae than homogeneously mixed waters.