Evaluation of co-fermented apple-pomace, molasses and formic acid generated sardine based fish silages as fishmeal substitutes in diets for juvenile European sea bass (Dicentrachus labrax) production

Abstract

Due to a need to address the potential of converting overfished sardines in North Africa and Middle East into a stable product, whole sardines were ensiled using different methods, and subsequently tested in a feeding trial and sequential digestibility assessment performed on sea bass, an important farmed fish of this region.Four isonitrogenous and isocaloric experimental diets were formulated for juvenile European sea bass replacing the fish meal protein component of a control diet with an apple pomace fermented fish silage (APFS); molasses fish silage (MFS) and formic acid silages (FAFS). Feeding sea bass with fish silage based diets generated similar or lower growth performance, feed utilization, protein efficiency and retention compared to the fish meal based diet. Hematological parameters were also measured at the end of the feeding trial. However, a significant difference (P < .05) was observed between the FAFS fed group and fermented fish silage treatments except for the APFS group with respect to leukocyte levels. Formic acid silage fed sea bass, showed more complicated mucosal fold features with greater depth, regularity and overall surface area (gut perimeter ratio) being significantly different (P < .05) compared to the control group. The apple pomace silage resulted in fish having the lower gut perimeter ratio.Scanning electron micrographs (SEM) of the distal intestine revealed that sea bass fed with all experimental diets showed no evidence of mucosal epithelial damage with all fish having healthy and regular shaped enterocytes lining the posterior intestine.However the microvilli gut enterocyte layer of sea bass fed apple pomace fish silage appeared thinner compared to all other treatment groups of sea bass. The study showed no evidence of any impaired general hematological changes indicative of health status of sea bass at the end of the trial period.In a consecutive digestibility evaluation, the apparent digestibility coefficient of dry matter (ADCdry matter) of the experimental diets was found to be relatively lower than the control group. However, the apparent digestibility coefficients for protein (ADCprotein) and energy (ADCenergy) were deemed acceptable for all silages tested.The overall findings of this study indicate that fish silage produced from organic acids or by fermentation with carbohydrate sources and lactic acid bacteria were an effective partial replacement of fish meal in aquaculture feeds. We show that this has potential for applications in diet formulations for European sea bass being an important farmed Mediterranean marine species.