Résumé
Globally, several seaweed species are reported to have great potential as functional ingredients in aquafeed for a variety of fish species, including Solea senegalensis, Clarias gariepinus, Salmo salar and Oreochromis niloticus. Ulva has been cultivated by the South African abalone industry in Integrated Multi-trophic Aquaculture (IMTA) systems for use as feedstock or crop-based dietary ingredients in formulated feeds for aquacultured abalone (Haliotis midae) for almost two decades, and more recently for sea urchins (Tripneustes gratilla and Parechinus angulosus). The current study aims to enhance the growth, immunity, oxidative stress, gut morphology and microbiome of Argyrosomus japonicus (dusky kob) through dietary supplementation with dried Ulva lacinulata. Dried U. lacinulata inclusion levels of 5, 10 and 15% (w/w) will be tested and compared with a non-supplemented (0% Ulva) control feed, totalling to four (4) dietary treatments- of 3 replicate tanks each. Data will be collected for (1) growth performance, and nutrient utilization: Weight gain, feed conversion ratio, specific growth rate, condition factor, hepatosomatic index, viscera-somatic index and survival rate; (2) Haematology: blood glucose, haematocrit and blood histology; (3) Immune response by assessing variation in the expression of relevant immune genes such as IL-1 bêta, IL-10, TNF-alpha and IgM from selected tissue samples (liver, intestine, head kidney and spleen). This will be conducted using semi-quantitative Real-Time Polymerase Chain Reaction (RT-PCR); (4) Flesh proximate analysis; (5) Antioxidant indicators of serum and liver; (6) Histology of the intestine; (7) Microbiome associated with gut tissue. Results from this study will help inform the aquaculture industry about how dietary Ulva-supplementation can help improve the health and welfare of one of South Africa's promising aquacultured fish species, the dusky kob A. japonicus. The presentation will provide an overview of the work that is planned and currently underway.