A Solid-State Fermentation (SSF) supplement improved performance, digestive function and gut ultrastructure of rainbow trout (Oncorhynchus mykiss) fed plant protein diets containing yellow lupin meal

Abstract

A nutritional investigation was conducted to determine whether growth performance, feed efficiency and midgut morphology of rainbow trout (Oncorhynchus mykiss) is affected by United Kingdom cultivars of Yellow Lupin (Control, Y) (LC) compared to the addition of a commercial solid-state fermentation product (SSF) in separate dietary treatments 0.1 and 0.5% (LS0.1 and LS0.5, respectively). At the end of feeding trial, LC- and LS0.1-fed fish did not differ from one another, whilst significant improvement was observed in LS0.5 fed fish (P < 0.05). Apparent digestibility of crude protein and crude fibre were significantly higher in fish fed LS0.1 and LS0.5 than LC. No significant differences (P < 0.05) in Haemoglobin (Hb) concentrations were observed among dietary treatments. Fish fed the 0.1% SSF inclusion exhibited significantly (P < 0.001) higher haematocrit (Hct) concentration than all other treatments. Significantly (P < 0.005) higher serum glucose levels were observed in FMC fed fish compared to fish fed LC and LS0.1, whilst elevation was also observed in LS0.5 over LC and LS0.1. Activity of serum lysozyme was significantly (P < 0.05) higher in the LS0.5 treatment compared to LC, S0.1 and FMC groups. Fish fed 0.5% SSF were observed to have a significant (P < 0.05) reduction in goblet cell counts (GC) compared to those fed LC and LS0.1.). Median enterocyte height (EH) of LS0.1 and LS0.5 fed fish did not differ from one another but were both significantly greater than LC fed fish. Mean microvilli length (MVL), diameter (MVD) and enterocyte apical area (EAA) did not differ significantly between dietary treatments (P > 0.05). Fish fed 0.5% SSF displayed a higher microvillar percentage coverage (MVCV) compared to fish fed LC and LS0.1. Total alkaline protease (TAP), trypsin and chymotrypsin activities in the digesta of fish were unaffected by dietary treatment (P > 0.05). Activity of alkaline phosphatase (ALP) in digesta was significantly (P < 0.05) higher in SSF treatments than LC. Activity of L-leucine aminopeptidase (LAP) in digesta was marginally significantly (P = 0.045) higher in LS0.1 SSF fed fish than LC fed fish. Activity of LAP was also significantly higher in LS0.5 fed fish than LC fed fish.