Developmental changes in body weight and elemental composition of laboratory-reared larvae of the red frog crab,Ranina ranina (Decapoda: Brachyura)

Ranina ranina larvae were reared at 29°C from hatching to the megalopa stage to measure daily changes in body weight, water content and elemental composition. Energy, estimated from carbon content, was also examined. The water content was 85 to 92% of body weight immediately after ecdysis but decreased with days after ecdysis. Gains in body weight, carbon, nitrogen, hydrogen and energy during each instar ranged from 52 to 245% and increased with instar after instar II (body weight and carbon), instar III (hydrogen and energy), and instar IV (nitrogen). Cumulative gains of these elements from hatching to 2 d before metamorphosis into megalopa ranged from 11 567% (carbon) to 12 209% (energy). Most cumulative gains (57 to 59%) in elemental composition were contributed by instar VII. Carbon, nitrogen and hydrogen content in body weight decreased to a minimum on the day of ecdysis and increased on the subsequent days. C:N ratios after instar IV were lowest on the day after ecdysis and reached a plateau by the second day. Energy, estimated as J mg^-1 dry weight (DW), decreased with instar and within a molt cycle, and was at a minimum on the day after ecdysis. Gains in elemental composition could be described by an exponential function of days after hatching and by a quadratic function in each instar.