Pre-Treatment of Fish By-Products to Optimize Feeding of Tenebrio molitor L. Larvae

SIMPLE SUMMARY: The rapid population growth and the consequent increase in demand for protein-rich foods pose a challenge for the food industry. On the other hand, resources are limited and production must be sustainable. Currently, insects are accepted by the European Union as sustainable and nutritive food for humans, consequently allowing the use of seven insect species, including Tenebrio molitor (Linnaeus, 1758). From a nutritional point of view, T. molitor is rich in protein (42.2–67.7%) with a good ratio of essential amino acids. However, their lipidic fraction lacks n−3 long chain polyunsaturated fatty acids (LCPUFAs), while it is rich in n−6 polyunsaturated fatty acids. This poses a problem for human intake, since the beneficial effect of n−3 polyunsaturated fatty acids and a low n−6/n−3 ratio on the prevention of cardiovascular inflammation and heart disease is well known. The present study is focused on the improvement of the fatty acid profile and proximal composition of T. molitor larvae through fish discard-based diets subjected to different pre-treatments to increase the fish-based diet intake. ABSTRACT: Fish discards are organic waste with high and good-quality protein levels, as well as a fatty acid profile rich in n−3 LCPUFAs, mainly eicosapentaenoic acid and docosahexaenoic acid. These discards can be used as food for Tenebrio molitor (Linnaeus, 1758) larvae, thus increasing the nutritional value of this insect. This study focused on increasing larval acceptance of fish through different pre-treatments of the diets provided, as well as increasing the accumulation of EPA and DHA in fish-fed larvae. Four different diets were prepared: control (broiler feed), DGF50: 50% dried ground fish (Pagellus bogaraveo, Brünnich, 1768) + 50% broiler feed, for different periods, FGF100: 100% fresh ground P. bogaraveo and DUF100: 100% dried whole unground P. bogaraveo. Growth, mortality, proximate composition, fatty acid profile and lipid nutritional indices were determined. Larvae fed with FGF100 displayed better results among treatments, doubling the initial weight, as well as increasing their protein level and decreasing fat levels. Regarding fatty acids, eicosapentaenoic acid and docosahexaenoic acid were only detected in larvae fed with a fish-based diet for a period longer than 5 days. These results show that pre-treatment of fish-based diets causes changes in the growth and compositional parameters of T. molitor larvae.