The effect of temperature on gonad, embryonic development and survival rate of juvenile seahorses, Hippocampus kuda Bleeker

This investigtion examined the effect of varying temperatures on the gonad development and the reproduction efficiency of Hippocampus kuda Bleeker. We demonstrated that gonad development, gonadosomatic index (GSI), female and mate fecundity, fertilization rate, hatching rate, and survival rate of juvenile seahorses varied significantly at different temperatures (18, 20, 22, 24, 26, 28, 30 and 32 degrees C). The periods of gonad development also differed significantly at different temperatures (F-7,F-32 = 154.065, P < 0.01). The optimal temperature was 28 degrees C based on the shortest developmental duration to stage V (mean standard deviation) (85.2 +/- 6.3 7 days). The GSI peaked at 28 degrees C (16.60 +/- 0.43%) and it displayed significantly higher than those of other seven trials (P < 0.01). The relationship between the GSI and the temperatures can be expressed by the following formula: Y = -1.0737t(2) + 8.0768t + 1.013 (r(2)=0.9894, n=30, P < 0.01). In contrast, the treatments could not develop successfully at 18 and 20 degrees C, ending before stage 11 and stage 111, respectively. The range from 26 to 28 degrees C was suggested as the optimal temperature for fecundity and spawning of H. kuda because of the large number of eggs in the ovaries. The relationship between fecundity number and temperature can also be formulated: Y=-30.536t(2) +209.24t + 237.8 (r(2)=0.886, n=30, P < 0.01). There were dramatic differences for fertilization and hatching rate among different treatments (F-5,F-24=53.675; F-5,F- 24= 101.897, P < 0.01). Compared with control seahorses, the results indicated that the condition indices such as the GSI, fecundity, spawning, fertilization, and hatching during the early development could affect in part the survival rate of the newborn juveniles (which was also an indirect effect of temperature). However, there were no marked differences at temperatures from 24 to 28 degrees C with the similar high survival rate. Based on this, the temperature range from 26 to 28 degrees C was recommended for gonad development and artificial reproduction of H. kuda. (c) 2005 Elsevier B.V. All rights reserved.