GROWTH AND PHYSIOLOGY OF CARCINUS-MAENAS (DECAPODA, PORTUNIDAE) LARVAE IN THE FIELD AND IN LABORATORY EXPERIMENTS

The principal aim of this study was to test if biochemical and physiol ogical data on decapod crustacean larvae from laboratory experiments c an be used for the interpretation of comparable field data. Different parameters measured under identical conditions in laboratory-reared an d field-collected larvae of Carcinus maenas were compared with each ot her. The parameters used were: dry weight (W), elemental composition ( C, N), protein and lipid content, activities of digestive enzymes (amy lase, trypsin), respiration, and ammonia excretion. Effects of differe nt laboratory diets (Artemia sp., diatoms and no food, representing ne ar optimal, suboptimal and starvation conditions respectively) were ev aluated as a possible base for the interpretation of field data. Field data were in a similar range to laboratory data, with the exception o f dry weight and protein:lipid ratio. Comparison of pooled data sets f or total larval development showed lower nitrogen and higher protein c ontents (in % of W) in field samples than in laboratory cultures, resu lting in different N:protein relations. Best agreement in these parame ters was found between field data and laboratory data from phytoplankt on-fed or starved larvae, whereas exclusively Artemia-fed larvae showe d higher percentages of C, N, and lipid. Larval W in stages later than zoea Il was consistently higher in the field. The protein content (in mug ind.-1) was higher in the field as compared with laboratory cultu res, resulting in a lower lipid:protein ratio. Comparison of lipid dat a and digestive enzyme activities under different nutritional conditio ns in the laboratory and in field samples shows that nutrition is limi ted in the field, and phytoplankton may constitute a major component o f the natural diet of C. maenas larvae. This conclusion is confirmed b y direct evidence from gut fluorescence and scanning electron microsco pic (SEM) examination of faecal pellets. Our study suggests that labor atory data on the physiology and biochemistry of decapod larvae may be a useful tool for the evaluation of field data.