Insects are promising bioconverting organisms and they can play a major role in addressing the issues related to organic wastes worldwide. A promising insect is the black soldier fly larvae (Hermetia illucens, BSFL), which can convert organic wastes into raw materials for animal feeds. However, BSFL meal production process results in large amounts of oil as a by-product. The oil from BSFL is rich in saturated fatty acids (SFAs), and lauric acid (LA, C12:0) is the predominant fatty acid. It has been previously reported that dietary lauric acid supplementation can reduce the proliferation of pathogenic microorganisms in the fish gastrointestinal tract, inhibiting inflammation and stimulating growth performance. Thus, the present study evaluated the potential of BSFL oil as a substitute for catfish oil in diets of hybrid catfish juveniles.
Nine hundred hybrid catfish juveniles (~17.4 g initial weight) were equally distributed in 30, 110- L aquaria, operating as a recirculating system. Experimental diets were formulated to be isoproteic (40% of crude protein) and isocaloric (20.45 MJ kg-1 of digestible energy) containing BSFL oil as a substitute for catfish oil at 0, 25%, 50%, 75% and 100% replacement levels . Fish were fed to apparent satiation twice a day for 60 days. At the end of the feeding trial, fish had ~474% weight gain, and s ignificant differences were observed for weight gain (P=0.03) (Figure 1), feed efficiency (P=0.004) , viscerosomatic indices (P=0.03) and total weight gain (P=0.01). No differences were detected for the hepatosomatic index, intraperitoneal fat ratio, hematocrit, hemoglobin, and feed intake. Fillet samples were collected for fatty acid analysis and results are pending. Fish were fed their assigned experimental feed for an additional week, and digesta samples were collected fro m the posterior segment of the intestine, and DNA was extracted for 16S rRNA sequencing. The intestinal microbiome results are also pending. At the end of the experiment, all fish were moved to a flow-through system, and they were subjected to a bacterial challenge using 7 × 106 CFU/g of Aeromonas hydrophila delivered through intraperitoneal injection. The dietary treatments did not have a significant effect on survival after the bacterial challenge. It can be concluded from the preliminary results of this feeding trial, that up to 50% of the catfish oil can be replaced with BSFL oil without any detrimental effects on production performance or compromising the disease resistance of hybrid catfish juveniles against A. hydrophila.