Utilization of IMTA-produced Ulva lactuca to supplement or partially replace pelleted diets in shrimp (Litopenaeus vannamei) reared in a clear water production system

Abstract

Integrated multi-trophic aquaculture (IMTA) systems typically rely on macroalgae to maintain water quality for fed and extractive species. Macroalgae harvested from these systems can in turn be used as feed source for these species. This study evaluated the use of harvested Ulva lactuca from a land-based IMTA system as a partial replacement (25, 50%) or a supplement (25%) to a commercial shrimp diet for Litopenaeus vannamei juveniles. In addition to the impacts on shrimp production, the nutritional profile of the commercial diet and the macroalgae were compared. Thirty shrimp (1.17 ± 0.12 g) were stocked in 80-L tanks in a clear water system and fed either a commercial pellet (100F), a commercial diet supplemented with U. lactuca (100F:25U), or a partial replacement diet (75F:25U, 50F:50U) for 7 weeks. Survival was similar in all treatment groups; however, all growth parameters were significantly lower in the 50F:50U group, although feed conversion ratio was also lowered. The harvested Ulva contained high levels of protein (32%) and a similar amino acid profile to that of the commercial diet, although lipid levels were low (1.9%), and docosahexaenoic acid (DHA) was lacking. Shrimp in the partial replacement treatment groups had significantly lower protein levels. These results indicate that up to 25% of a commercial diet may be replaced with fresh U. lactuca without impacting shrimp production, and therefore, a cost savings in feed may be seen in an IMTA system producing both shrimp and Ulva.