Insect meal and single cell proteins as alternative sources to fishmeal in diets for gilthead seabream (Sparus aurata) juveniles

Abstract

The main objective of this project was to look for alternative ingredients to fishmeal, given that it is a highly demanded and finite resource as it is the main component of numerous food products. Thus, it is necessary to find alternatives that meet the requirements of aquaculture fish and maximize fish growth and health. In order to meet the goal proposed, two alternative ingredients with a great potential as protein source for fish were tested: insect meal (Hermetia illucens) that replaced fishmeal in 33.33% (5-INS diet) and 66.66% (10-INS diet), and single cell protein (a by-product generated by Methylococcus capsulatus' fermentation) that substituted fishmeal in 33.33% in two diets containing this ingredient (5-SCP and 10- SCP), in addition to another 33.33% substituting plant meal in the second diet (10- SCP). Gilthead seabream Sparus aurata juveniles, with an average of 65.37 grams of weight were fed to apparent satiation three times per day for 89 days, monitoring its growth performance every 29 days. At the end of the nutritional trial, growth performance indicators were calculated, and samples were taken for gene expression, plasma lysozyme content and digestive enzyme activity studies. Fish fed 5-INS and 10-SCP diets showed similar growth performance as those fed CTRL diet. In contrast, 10-INS diet led to a reduction in growth parameters and feed utilization of fish. Even tough, none of the experimental diets affected the digestive enzymes activities, plasma lysozyme content or expression of any of the health-related genes measured in posterior gut. The results of this study showed that insect meal from black soldier fly (Hermetia illucens) can be up to 5% in replacement of fishmeal, and SCP obtained from the bacteria Methylococcus capsulatus up to 10% in replacement of fishmeal and plant protein sources without negatively affecting growth performance, feed utilization, digestive enzymes or fish health.