Resumen de Feeding strategies and rearing techniques for a sustainable aquaculture
The present PhD thesis aimed at improving the knowledge on feeding strategies and rearing techniques that might improve the sustainability of the aquaculture sector through a multidisciplinary approach, evaluating fish growth performance, health and quality, and vegetable production. The environmental impact of the different solutions was also assessed using a Life Cycle Assessment (LCA) analysis as a part of thesis general discussion. The first contribution evaluated how replacing different levels of fish oil by vegetable oils in the diet of Mediterranean yellowtail, Seriola dumerili (Risso, 1810), affects the fatty acids (FA) signature, i.e. overall FA profile, in different tissues. The FA signatures of red and white muscle, liver, and visceral fat tissues changed when the dietary FA source changed, whereas FA signatures in the brain were rather robust to such dietary changes. The second contribution assessed the effects of a wash-out on the fatty acid composition in the muscles of Mediterranean yellowtail. A 90-d wash-out can partially improve the FA profile in muscles of Mediterranean yellowtail previously fed vegetable oil-based diets. The third contribution investigated the effects of two stocking densities (low - ALD, 3.81 kg m¿3 vs. high - AHD, 7.26 kg m¿3) on the growth, health, and flesh quality of rainbow trout (Oncorhynchus mykiss, Walbaum 1792) and the yield and microbiological quality of lettuce (Lactuca sativa, L.) produced in a low-tech aquaponic system compared to hydroponic cultivation (HYP). Rainbow trout and lettuce productions were successful in the tested aquaponic system, whereas stocking density did not affect fish growth or flesh quality. The fourth contribution evaluated the effects of dietary substitution of fishmeal with partially defatted (Hermetia illucens, Linnaeus, 1758,) meal (HI) on the growth, feed digestibility, gut morphology, and fillet quality of rainbow trout reared in a low-tech aquaponic system fish growth and fillet quality were essentially unaffected by a 25% fish meal replacement with HI, whereas at a replacement rate of 50%, certain effects on gut histology and fillet colour and nutritional characteristics were detected, which warrant further investigation.
In conclusion, based on the results of the present thesis, vegetable oils and insect meal are promising alternative ingredients to be included in diets for high-value marine and freshwater carnivorous species. Nevertheless, future aquafeed formulations will be required to focus not only on the nutritional characteristics and costs of the ingredients but also on their environmental impact. Aquaponics is a promising technique to be used for rearing high-value freshwater species such as rainbow trout. Furthermore, the optimization of fish stocking density in aquaponics is a key aspect to obtain high product yields and quality, reducing the environmental impact as well as assuring fish health and welfare.
