Response of early-stage spiny Jasus edwardsii phyllosoma larvae to changes in temperature and photoperiod

The influence of temperature and photoperiod on the survival, intermoult period, moult increment and feeding activity were examined in early stage Jasus edwardsii phyllosoma larvae. In the first experiment, growth increment of newly-hatched larvae to Stage II was similarly high after rearing at 14.3 and 18.2 °C and lowest at 10.5 and 21.5 °C, whereas survival to Stage II was not significantly different between temperatures. By contrast, almost all Stage II phyllosoma died at 21.5 °C but there was no difference in survival from Stages II to IV at 14.3 and 18.2 °C, while larvae at the coldest temperature (10.5 °C) did not moult beyond Stage II during the experiment. The biological zero temperature of Stage I larvae was estimated at 9.4 °C by the Bělehrádek's expression fitted to the relationship between intermoult period and temperature (V = 48.716 (T - 9.425) - 0.579). The growth rate and moult increment remained greater at 18.2 °C than at 14.3 °C throughout subsequent development to Stage IV. Consumption of Artemia nauplii by Stage I larvae escalated from 10.5 to 18.2 °C but not at higher temperature. An energetic imbalance at 21.5 °C may explain the reduced growth in Stage I larvae compared to animals reared at 18.2 °C. In the second experiment, daily photoperiods with 0, 6, 12, 18 or 24 h light did not affect larval survival through the first three stages of development but had a marked effect on intermoult period, growth and feeding. The response to increasing photoperiod changed during development, with Stages I and II larvae tending to grow faster and feed more under increasing light conditions whereas Stage III larvae required some light/dark phase to optimise growth (shortest intermoult period and highest moult increment at 6, 12 or 18 h light) and feeding. These findings will assist in refining the culture conditions for early stage J. edwardsii larvae. © 2008 Elsevier B.V. All rights reserved.