Biochemical and technical observations supporting the use of copepods as live feed organisms in marine larviculture

Abstract

The use of live prey is still necessary for a large number of raised fish species. Small sized rotifers are usually used as live preys during the first days of feeding in small mouth fish. An alternative to this is the use of copepods as prey for first feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30–32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23–32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35–1.63 in copepods). The FAA pattern of the preys tended to be species-specific and its implications from an aquaculture point of view is discussed. In contrast, the-protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on ‘the price’ of hatching in Acartia tonsa eggs before or after cold storage at 3°C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.