Maturation of Hippocampus guttulatus and Hippocampus hippocampus females by manipulation of temperature and photoperiod regimes

The present study provides new and practical information on the maturation of females seahorses Hippocampus guttulatus and Hippocampus hippocampus exposed to different temperatures (15 °C constant, 15-18 °C or 15-21 °C) and photoperiods (10L:14D-16L:8D cycle or 10L:14D constant). Egg production (total eggs, clutch size and clutches per female) resulted notably reduced under both short photoperiods and low temperature, especially in H. guttulatus. Egg clutches were mainly released with temperatures above 16 °C and increasing photoperiods beyond 14L:10D. The highest efficiency under a natural light regime was achieved at 21 °C. Biometrics performed in H. guttulatus eggs showed that egg volume (VE) was not affected by temperature level but yolk volume (VY) and VY/VE ratio in eggs of females exposed at 15 °C were lower than in eggs released at 15-18 °C and 15-21 °C cycles. VE, VY and VY/VE in eggs were not correlated with the photoperiod regimes applied. The present study also provides the first results on shifting of maturation in H. guttulatus females submitted to photothermic manipulation of the environment (Treatment D - advanced and drastic change; Treatment A - advanced and accelerated change) or to natural conditions (Treatment N). The response of females to artificial environmental changes was successful and fast. First egg clutches in treatments D and A were released 11 (Treatment D) and 9 (Treatment A) weeks before than in females exposed to natural temperature and photoperiod regimes. However, the best overall results were achieved under natural regimes. In Treatment N, total eggs production and average egg clutch size (3690 and 461 eggs, respectively) were noticeable higher than in treatments D (3533 and 294 eggs, respectively) and A (150 and 1809 eggs, respectively). The study demonstrates the feasibility of shifting in female maturation of seahorses and its practical use in the artificial manipulation of the breeding season under captive conditions.