A feasible path towards year-round production: Effects of temperature and photoperiod on ovarian maturity of subtropical palaemonid, the river shrimp, Cryphiops caementarius

Abstract

Throughout the last decade, crustacean aquaculture has been developing rapidly worldwide and has given rise to a growing global trend demanding freshwater native species that share both, socio-economic importance and commercial interest such as subtropical and temperate palaemonids. Unfortunately, the reduction of native populations and the partial or complete absence of ovigerous females during the months of autumn and winter are serious obstacles towards a successful, responsible, and profitable cultivation of such palaemonid species. When reviewing the natural environment at the start of the reproductive season, an increase in both, water temperature and daylight is easily perceived, thus we decided to investigate their effects (temperature and photoperiod) on the ovarian maturation in a subtropical freshwater palaemonid of commercial interest (Cryphiops caementarius) with promising results for a strong and prosperous commercial cultivation. Adult females of C. caementarius were randomly distributed among four treatment groups (G1, G2, G3, and G4). The study was developed in two phases, an initial conditioning phase in which the four treatment groups were exposed to winter environmental conditions for 42 days (photoperiod 10 L:14D, temperature 13 °C) and a final test in which each group was exposed to a specific combination of photoperiod and temperature for a term of 105 days: G1-winter photoperiod and winter temperature (10 L:14D, 13 °C), G2-summer photoperiod and summer temperature (14 L:10D, 25 °C), G3-summer photoperiod and winter temperature (14 L:10D, 13 °C), G4- winter photoperiod and summer temperature (10 L:14D, 25 °C). All the females were individually marked and the events of maturity and spawning were monitored. Maturity events were not recorded in any of the treatment groups exposed to winter temperatures, while 39 % and 31 % of the females exposed to summer temperatures in G2 and G4 respectively, had at least one maturity event during the testing phase. The results obtained suggest that an increase in temperature could be the environmental cue responsible for triggering the process of ovarian maturity in C. caementarius and that an adequate thermal control would allow the production of ovigerous females during the winter months. Controlling crustacean reproduction in captivity using environmental variables instead of invasive techniques such as eyestalk ablation or hormone injection opens a feasible path towards recovering natural populations and/or consolidating commercial farming through friendly aquaculture procedures.