Optimizing Feeding Regimes and Vitamin Delivery Methods in Microdiet for Improving Survival and Growth of Carp Larvae

In pond carp production, there is growing interest in producing larvae out of season to shorten the production cycle and increase profitability. For this reason, carp fries are produced in indoor recirculation systems, where larvae are fed Artemia salina. Due to the limited ability of fish larvae to digest conventional microdiets-attributable to their short, agastric intestines-live feed remains essential. Therefore, the encapsulation of micronutrients, such as vitamins, may improve delivery efficiency. To address these challenges, three trials were conducted with the following aims: (i) to develop the most effective weaning strategy; (ii) to evaluate the best encapsulation method for vitamin delivery to larvae; (iii) to test different protein sources in microdiets; and (iv) to assess the effectiveness of vitamin supplementation under stress conditions. The data on production parameters demonstrated that feeding common carp larvae with Artemia for 8 days, followed by a 4-day co-feeding period, is necessary to initiate the utilization and nutrient uptake from microdiets. Regarding vitamin delivery via encapsulation technology, better performance was achieved when proteins were used as encapsulating agents compared to oil-based carriers. Additionally, the survival rate of fish fed with plant-based microdiets was significantly lower (66.2% ± 11.2%) than that of larvae fed with fish-based diets (91.1% ± 3.0%) at 32 days post-hatch (dph). With respect to vitamin supplementation, enrichment with water-soluble vitamins (WSVs) was not detected in fish larvae; however, a slight association was observed between antioxidant vitamin levels and stress markers. In conclusion, fish-based microdiets show strong potential as a substitute for live feed in indoor carp larval rearing from 12 dph onward. However, further development of the encapsulation process is necessary to improve the delivery efficiency of WSV.