The effects of food and the sum of effective temperature on the embryonic development of the seahorse, Hippocampus kuda Bleeker

Abstract: The effect of different food (live Acetes spp., live Mysis spp., frozen Mysis spp., and mixed food of 50% live Acetes spp. and 50% frozen Mysis spp.) on gonad development of seahorses, Hippocampus kuda Bleeker, was evaluated in this experiment. The developmental durations of testes and ovary of seahorses were significantly different among the four experimental treatments. The live Acetes spp. treatment presented the shortest developmental durations to stage V, which were 87.6±3.84 days and 89.2±3.71 days, respectively, for ovary and testes. The frozen Mysis spp. treatment had the longest developmental durations (F 3,15 =13.284, P <0.05). The relationship between developmental duration of the ovary and gonad developmental stages could be formulated: Y 1 =12.04x +24.36 (r 2 =0.9722, n =16, P <0.05). The gonadosomatic index (GSI) of parent seahorses among the four treatments differed significantly (F 3,15 =18.364, P <0.05). The standard GSI of seahorses fed live Acetes spp. was 15.64±1.65%, which was the highest. Feeding live food had a significant effect on the fecundity and spawning of seahorses. The fecundity and spawning number of the live Acetes spp. treatment were 598±45.49 and 552±49.19 individuals, respectively, which were dramatically higher than those of frozen treatment (F 3,19 =34.152, P <0.05). Live food also had a similar effect on the fertilization and hatching rate during the embryonic development of seahorses (F 3,19 =11.386, P <0.05). Food treatment could also induce an indirect effect on survival rate of juveniles through gonadal and embryonic development of the parents (F 3,15 =14.519, P <0.05). In this experiment, the mortality within parent seahorses in the frozen Mysis spp. treatment was the highest (15.1±6.55%), and the survival of juveniles was the highest in the live Acetes spp. treatment (90.4±2.26% at 10 days). In conclusion, feeding live Acetes spp. significantly benefited the gonadal and embryonic development of H. kuda. The effect of temperature (22 °C, 24 °C, 26 °C, 28 °C, 30 °C and 32 °C) on the hatching time of H. kuda was also studied. We demonstrated that the higher the temperature, the shorter the hatching time, as well as the higher the hatching speed. The relationship between hatching time and temperature could be expressed: T =−39.337 t +677.75 (r 2 =0.9755, n =30, P <0.05). In this finding, we provided the sum of effective temperature (SET) and threshold temperature of embryonic development of H. kuda (14066.9 °C h−1 and 13.7 °C, respectively). This new information on the effect of feeding type and culture temperature is beneficial for the commercial rearing and breeding industry of this species. [Copyright &y& Elsevier]