Growth and Exuviation of Norway lobster (Nephrops Norvegicus) larvae reared in the laboratory

Abstract

Abstract Larvae of the Norway lobster, Nepbrops norvegicus L., were reared in the laboratory from hatching to the end of stage III (metamorphosis). Their growth was measured as fresh weight (FW), dry weight (DW), ash-free DW (AFDW), carbon (C), nitrogen (N), hydrogen (H), and energy (E, estimated from C). The same measurements (except FW) were made in larval exuviae. FW remains fairly constant in each larval stage, whereas all other measures of biomass or energy increase. Growth during each moult cycle can be described by power functions of time. Body composition of the larvae shows some regular changes: water content (% of FW) and ash (% of DW) decrease during each moult cycle and increase again at ecdysis. The fractions of C, Nand H (% of DW) do not show clear changes during single stages, but a slight decreasing tendency from the first to the last larval instar, with mean values of 33–39% in C, 7–10% in N, and 5–6% in H. These results suggest a relatively constant biochemical composition of N. norvegicus larvae during development. Production of biomass and energy (in mg or Joules per individual) increases from the first to the last stage. The opposite trend is found when production during an instar is expressed as percentage of early postmoult values. That part of production which is lost again at ecdysis (the turnover rate) increases from insrar to instar, and it is highest in DW, intermediate in AFDW,C, H, and E, and it is lowest in N. The same trends are found when exuvial losses are related to late premoult biomass or energy: 17–25% of DW, 9–16% of AFDW, C, H or E, and 5.6–7.5 % of N are cast with the exoskeleton. Growth and exuvial losses of N. norvegicus larvae are compared with literature data on another lobster species (Homarus american us) and further Decapoda.