24 JUNE 2024 • WORLD AQUACULTURE • WWW.WAS.ORG supplements, and probiotics, we have achieved a minimum survival rate of 81% during the initial 21 days post-hatching. Our focus extended beyond enhancing survival and production; we also sought sustainable methods for achieving these goals. Recycling waste nutrients generated by rotifer and larval culture facilitated the production of microalgae, which, in turn, served as feed for rotifers, creating a circular production system. We then explored strategies to maximize the utilization of the diverse products obtained from this circular production. Chlorella, a rapidly proliferating unicellular green algae, emerged as one of the products generated in this process. This microalgae boasts a high nutritional profile, including proteins (50% to 60% of its dry weight), carbohydrates (such as cellulose), lipids (including essential fatty acids like omega-3s), minerals (such as iron and magnesium), antioxidants (such as beta-carotene, lutein, and zeaxanthin) and vitamins (such as B-vitamins and Vitamin C). While most animals can produce Ascorbic Acid from glucuronic acid, fish and crustaceans lack the enzyme gluconolactone oxidase needed for the final step in this process (Chatterjee 1973, Dabrowski 1990). As a result, they rely on consistent dietary sources of vitamin C. Vitamin C is key for adequate growth enhancement, reduction of skeletal deformities, mitigation of stress effects, immune system support, and antioxidant protection. Currently, fish larvae in aquaculture primarily depend on commercial live feed supplements to meet their vitamin C needs. Considering the high vitamin C (118 mg/100gr) content in Chlorella vulgaris, we investigated the potential production to meet the market demands. As is the case for many other species, such a quest confronts a series of hurdles along the way, mostly related to the earlier developmental stages (larval and fry). Traditionally, larvae and fry obtained all the nutrients from the diverse planktonic organisms found in the ponds during the summer months, and replicating such ideal conditions in indoor RAS represents a challenge. Prey selection and matching nutrient requirements are among the biggest challenges. Pikeperch larvae exhibit physiological resemblances to certain marine species counterparts, notably in their small hatching size (approximately 4-5 mm), limited tolerance to environmental fluctuations, and propensity for early cannibalism. Conventionally, Artemia has been the primary live feed species; however, this feeding protocol inadequately addresses the smaller larvae within the cohort, with only 30-35% capable of consuming Artemia due to their size being larger than the mouth gape. Recent research conducted at our Institute has yielded promising outcomes (Imentai et al. 2019 a,b, Yanes-Roca et al. 2018, 2020 a,b) by introducing rotifers as the initial feed source. This approach, commonly employed in many marine species, has enabled the feeding of 100% of the larvae during the first 10 days. This introduction not only overcomes physical barriers (size) but also utilizes rotifers as an ideal vehicle for delivering tailored nutrition during this critical developmental phase. Through a series of trials involving various rearing techniques, nutritional PHOTO 2. The Institute for Intensive Aquaculture at the University of South Bohemia has been working with pikeperch culture for more than three decades.
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