A STUDY ON THE HISTOLOGICAL CLASSIFICATION OF THE IN-SITU NUTRITIONALCONDITION OF LARVAL SOUTH-WEST ATLANTIC ANCHOVY, ENGRAULIS-ANCHOITA HUBBS AND MARINI, 1935

During cruise 11 of the R.V. Meteor in autumn 1989 larvae of the South west Atlantic anchovy, Engraulis anchoita Hubbs and Marini, 1935, were caught in three areas of high hydrographic diversity in the South-wes t Atlantic. The study had two main objectives: 1) The determination of distinct histological indices of larval nutritional condition, 2) Com parison of the proportion of well and insufficiently fed fish larvae i n hydrographically differing environments. The samples were taken (1) in subtropical waters on the Brazilian shelf characterised by upwellin g events, (2) in a region off Uruguay which is influenced by the fresh water outflow of the Rio de Ia Plata, and (3) in a tidal mixing front on the Argentine shelf around the Valdez peninsula which is influenced by the cold Malvinas Current. Hauls were carried out in distinct dept h layers with modified MOCNESS equipment. About 1000 larvae were prepa red using standard histological techniques. As a result of a comparati ve histological study, cellular appearances of gut and liver were sele cted to be the criteria for larval condition. In addition, the height of the midgut mucosa was measured to be compared with the histological pictures. A simultaneous classification of organ development stages a llowed a stage specific comparison of the histological condition of in dividual larvae, the gut measurements, and finally the nutritional con dition. Evaluating the analytical methods applied, gut mucosa height h ad to be rejected as a criterion for larval condition, because it did not give significant results within and even between the developmental stages. Histological results showed that only 2 % of the larvae inves tigated had passed ''the point of no return and, therefore, could be c lassified as starved individuals. The 98 % remaining were composed of well fed larvae or of those having been reversibly emaciated. All of t he starved anchovy larvae were caught in Brazilian waters, and especia lly, the more developed stages showed symptoms of an insufficient food supply Although most of the starved larvae came from an offshore samp ling site, the results of the study did not confirm a clear relationsh ip between sampling site or depth and local hydrographical structures or prey densities. Reasons for regional variability in nutritional con dition and larval survival are discussed.