Sea cucumbers are a good candidate species for aquaculture due to their high dollar value and strong demand for human consumption and medicinal use. As detritovores they were considered as an extractive culture component for the HBOI-LB-IMTA system. Preliminary observations of the sea cucumber, Holothuria floridana, maintained in unfiltered system water suggested that they preferred fresh Ulva lactuca, over biofloc solids. Skin lesions were observed in some of the sea cucumbers, and amphipods, present in the unfiltered water, were postulated to be responsible. To better understand the impact of diet and water source on H. floridana production and lesion development, a 12-week 2x3 factorial experiment was designed.
Ten sea cucumbers (11.5+1.8g) were randomly added to one of twenty-seven 30-L square tanks placed into troughs, with a flow through system. Provided water sources were salt well water, filtered IMTA water, or unfiltered IMTA water. Pelleted diets were manufactured that replaced 20% of fish meal with biofloc or Ulva meal. Sea cucumbers were fed a 100% biofloc, 100% Ulva or 50% biofloc and 50% Ulva diet, twice per day at 5% body weight. Dissolved oxygen, temperature and salinity were taken daily and pH continuously. Ammonia, nitrite and alkalinity was measured twice per week. Mortality was assessed daily, and presence of lesions noted; individuals were weighed bi-weekly.
No significant difference was seen between treatments with regards to final growth or survival. Initially (wk 0-6), highest survival was seen in treatments receiving filtered water (93%), and lowest in treatments receiving unfiltered water (78%), but differences were not significant (P=0.0656). By week 8 survival was low in all treatments (53-77%), and following impacts bought on by Hurricane Dorian continued to decline; final survival was 27-60%. Growth initially increased in treatments receiving filtered water, regardless of diet, but decreased to initial weights by week 4, and continued to decrease in all treatments thereafter.
Amphipod presence and water chemistry may have initially played a role in terms of survival in the unfiltered IMTA treatment. Amphipods were an issue in 78% of unfiltered IMTA treatments, compared to 45% of filtered, and 18% of well water, and amphipod presence was associated with lesion development. Nitrites were higher and pH was lower in unfiltered IMTA treatments as well. However, low survival and negative growth were apparent in all treatments by week 8 indicating that other factors were responsible for poor production.