High quality post-larvae (PL) are required for the farming industry of whiteleg shrimp (Penaeus vannamei), and hatcheries continuously improve rearing and feeding protocols. The early rearing is a critical period in shrimp development, with the weaning from live-feeds to inert microdiets being strongly influenced by diet quality. Microdiet quality has a large impact on shrimp performance in the long-term, affecting the downstream production of high-quality juveniles. Therefore, there is room for optimizing a weaning diet for shrimp larvae/post-larvae, in particular to improve robustness. In fact, industrial shrimp farming is characterized by inconsistent yields as it is quite susceptible to pathogenic outbreaks. Once shrimp cannot be vaccinated and the use of antibiotics is legally limited in many countries, functional dietary additives can be used as a prophylactic alternative to stimulate the shrimp immune condition. This work summarizes the development of a functional premium microdiet boosting shrimp post-larval performance and quality.
Four trials were conducted with white leg shrimp PL (initial wet weight 3-13 mg) reared under standard procedures in triplicate tanks. Shrimp were reared at RIASEARCH Lda facilities (Portugal), at 27-28ºC, and fed on microdiets ad libitum for 18-21 days.
Firstly, the protein requirement at the post-larval stage was evaluated; 6 diets ranging from 34 to 63% crude protein were used. Results show a dose-response pattern for growth of shrimp PL (3-70mg wet weight), with a break-point at 47.1% dietary crude protein.
Protein sources were subsequently tested using 4 diets containing either fish meal, squid meal, krill meal or a balanced mix of these three (52% crude protein), as main ingredients. Results show no significant differences between treatments for final body weight, and survival was lower in the fish meal-based diet.
Functional additives were evaluated using 4 experimental microdiets: a commercial like diet as positive control (PC); a negative control diet (NC) based on PC but lower in vitamin C and E; the NC diet supplemented with taurine plus methionine (T+M); and the NC diet supplemented with β-glucans (BG). Results suggest dietary vitamin C and E to impact pathogen susceptibility, while
β-glucans seem to decrease lipid peroxidation, and boost the antioxidant and immune status.
Finally, the cost-effectiveness of 3 microdiet prototypes was then assessed. Results showed no differences for PL survival (75 - 87%) or economic feed conversion ratio, but shrimp PL fed an ultra-premium diet achieved a significantly higher final body weight and relative growth rate (19.8 %/day) than those fed the standard (15.6 %/day) or premium (17.1 %/day) diets.
In short, this study shows that: 1) A dietary protein requirement of 47.1% was established for shrimp PL (3-70 mg wet weight); 2) Squid and krill meals proved to be good sources of protein for the early development of shrimp, as well a mixture of these two with a high quality fish meal; 3) The use of functional dietary additives, such as β-glucans, vitamins C and E, bring benefits to the antioxidant capacity and immune condition of the shrimp PL; 4) Higher quality diets can be advantageous in early phases of production, leading to a reduction of time to reach commercial size, and savings in operational costs.
Acknowledgements: This work was part of the project FA_05_2017_005 SHELLWIN, financed by the Blue Fund program of the Ministry of the Sea, Portuguese Republic.