The bioinvasion of Portunus segnis, an invasive crab species in Tunisian waters, presents significant environmental challenges, and the management of industrial crab waste remains unresolved. This study addresses both issues by investigating the enrichment of fish feed for Nile tilapia (Oreochromis niloticus) farming using dried Portunus segnis crab shell waste, with the main goal of enhancing feed quality and improving aquaculture sustainability in Tunisia.
This study implied the formulation of fish feed using a balanced mix of animal-based fish meal sourced from sardines and plant-based meals, including soybean and maize flour. Dried crab shells from Portunus segnis were incorporated into the feed at varying percentages of 5%, 10%, and 15%. The feed formulations were prepared by thoroughly grinding the dried crab shells and mixing them with the fish meal and plant-based ingredients to ensure uniform distribution of nutrients. Afterward, feeding trials were carried out using juvenile Nile tilapia (Oreochromis niloticus), and the feed was randomly assigned to four groups: one control group and three experimental groups receiving 5%, 10%, and 15% crab shell-enriched feed, respectively. Fish were reared in controlled aquaculture systems provided with a consistent feed for 12 weeks. In addition, growth performance measures, including weight gain, feed conversion ratio (FCR), and survival, were recorded weekly. Moreover, lipid profiles, particularly the concentrations of polyunsaturated fatty acids (PUFAs), were analyzed using gas chromatography to assess the nutritional benefits of the crab-enriched diet.
As indicated in the figure, adding 10% Portunus segnis crab shell waste to fish feed significantly improved the mineral composition, raising calcium content from 2.5% to 6.3%. In addition, the biochemical analysis of the crab shells revealed a composition consisting of 29.7% calcium, 15% chitin, 1.8% magnesium, and 2.2% phosphorus, which contributed to the overall nutritional profile of the feed. Accordingly, adding crab shell waste improved lipid composition, resulting in increased concentrations of polyunsaturated fatty acids (PUFAs), particularly omega-3 and omega-6 fatty acids. Notably, the percentages of eicosapentaenoic acid (C20:5, EPA) and docosahexaenoic acid (C22:6, DHA) were increased significantly in the feed, with EPA levels reaching 1.8% and DHA levels at 1.2%. Moreover, the fish fed with the 10% crab-enriched diet exhibited a 12% higher growth rate and a 9% improvement in the feed conversion efficiency compared to the control group. Furthermore, the enhanced PUFA content in the feed contributed to better overall fish health, increasing their resilience and improving the quality of the final product.
Incorporating Portunus segnis crab shells into fish feed offers the dual benefit of controlling the invasive crab population and adding value to the fish feed industry by improving the nutritional quality of the feed. Thus, this sustainable approach can support aquaculture and the local Tunisian crab export market.