Notes: Gross Conversion Efficiencies of Mummichog and Spotfin Killifish Larvae from a Georgia Salt Marsh

Abstract

We conducted two experiments to determine gross food conversion efficiencies (K ₁) for larvae of two common salt-marsh fundulids, mummichogs Fundulus heteroclitus and spotfin killifish Fundulus luciae. Larvae were fed a known number of brine shrimp nauplii (Artemia sp.) daily in both experiments. In experiment 1, conducted at 27°C and with a 14-h light (L): 10-h dark (D) photoperiod, mummichog larvae had a mean daily specific growth rate (G, mg/mg) of 0.284 and a mean K ₁ of 34.7%. In experiment 2 (24°C, 12 h L:12 h D), mummichog larvae consumed less food and their growth rate was lower (G = 0.240), but there was no significant change in conversion efficiency (K ₁ = 37.8%). Spotfin killifish larvae, which were included only in experiment 2, were more efficient (K ₁ = 49.7%) and grew faster (G = 0.278) than mummichog larvae under the same conditions. There was a direct relationship between final larval weight and K ₁ for mummichogs but not for spotfin killifish. In contrast, final larval weight was directly related to total individual prey consumption in spotfin killifish but not in mummichogs. Based on our experimental data and comparisons between the length-weight relationships of field-collected and laboratory-reared larvae, we suggest that natural prey concentrations may be suboptimal for mummichog but not for spotfin killifish larvae.