Effects of water renewal rate on water quality of the hatchery system and larval survival, growth, and development of the sea cucumber (Holothuria leucospilota)

In this study, four levels of water renewal rates (0, 1/4, 1/2 and 3/4 per day, respectively) were used in sea cucumber Holothuria leucospilota hatchery. Water quality of the hatchery system and the larval survival, growth, and development of the H. leucospilota have been tested to evaluate the optimum water renewal strategy. The results show that, in the early stage, high water renewal rate could pose adverse impacts on larval survival and growth; while in the later stage, low water renewal rate, which correlated with high level of ammonia nitrogen (NH₃-N) and nitrite (NO₂-N) in the hatchery system, could also pose adverse impacts on larval survival and growth. The biological toxicity experiments were carried out to test the effects of (NH₃-N) on mid- and late-auricularia larvae at water temperature of 27.99 °C and pH of 8.05. The results show that, both the survival and development potential of the larvae were negatively correlated with the high NH₃-N concentration level. The 48 h-LC₅₀ of NH₃-N on mid- and late-auricularia were 2.66 and 6.22 mg/L, respectively, while the 48 h-LC₅₀ of un-ionized ammonia (NH₃) on mid- and late-auricularia were 0.19 and 0.45 mg/L, respectively. In summary, water quality was important for H. leucospilota hatchery, and effective measure must be taken to control the concentration of NH₃-N in the culturing water. It is recommended that no water change should be carried out at the early-auricularia stage, moderate water renewal at the mid-auricularia stage, and high water renewal at the late-auricularia stage.