Time‐related changes of the intestinal morphology of Atlantic salmon, Salmo salar L., at two different soybean meal inclusion levels

Abstract

Soybean meal (SBM) induces enteritis in the distal intestine of Atlantic salmon. The present study assesses the effects of SBM concentrations on the kinetics of the enteritis process. Fish of 300 g, kept at 12 degrees C, were fed diets with different SBM inclusions: 0%, 10% and 20% SBM for 57 days. Samples of the distal intestine of five fish per treatment were taken for histological and electron microscopical analysis. A semi-quantitative scoring system was used to assess the degree of the morphological changes induced by SBM feeding in the distal intestinal epithelium. The first signs of enteritis appeared earlier in the salmon fed the 20SBM diet than in those fed the 10SBM diet. Thereafter, the condition increased steadily, displaying no signs of recovery. Furthermore, at the lower concentration, the process marking the onset of enteritis began more gradually than at the higher concentration and it displayed a tendency to stabilize after 13-20 days of continuous feeding. Electron microscopy indicated that the endocytosis process was hampered at day 3 of 20SBM and at 7 days of 10SBM. Furthermore, a strong reduction of microvilli was already evident after 7 days of 20SBM feeding, thus indicating a decreased uptake capacity of the distal enterocytes. In addition, transformation and migration of eosinophilic granulocytes was observed, which, in combination with the lysozyme C immunoreactivity supports their protective role during the inflammatory process in the distal gut of Atlantic salmon. It can be concluded that the severity of enteritis and its kinetics are concentration-dependent, showing no signs of recovery during feeding with diets containing SBM.

Feeds, water quality, gut morphology and digestion in Nile tilapia (Oreochromis niloticus)

“…These changes in the intestinal morphology as a consequence of feeding SBM-based diets seem to be species specific, just as its ability to recover from these changes when fed a non-SBM-based diet. In Atlantic salmon, no signs of intestinal recovery of this SBM-induced enteritis occur with time (Urán et al, 2009). On the other hand, a recovery of the distal intestinal epithelium was observed in carp starting from 4 weeks onwards after continuously being fed a SBM-based diet (Urán et al, 2008a).…”

“…These changes in salmon may include: widening of the lamina propria and the increase of the presence of inflammatory cells such as lymphocytes, macrophages and leucocytes (Baeverfjord and Krogdahl, 1996); shortening of villi and microvilli (van den Ingh et al, 1991). These SBM induced changes have been classified as an enteritis response of the distal intestine (Urán et al, 2008b, Urán et al, 2009. Some of these changes have also been found in species other than salmonids, e.g., common carp (Cyprinus carpio) (Urán et al, 2008a), gilthead sea bream (Sparus aurata) (Bonaldo et al, 2008), summer flounder (Paralichithys dentatus) (Bone, 2013).…”

“…In comparison with the other tested ingredients, soybean meal caused significant negative changes in the intestinal morphology of Nile tilapia such as widening of the SM and LP, and an increase of the number of GC. Soybean is widely known to contain adverse anti-nutritional compounds which induce intestinal disorders in Atlantic salmon (van den Ingh et al, 1991, Baeverfjord and Krogdahl, 1996, Urán et al, 2009, rainbow trout (Heikkinen et al, 2006, Venold et al, 2012, or summer flounder (P. dentatus) (Bone, 2013). In Nile tilapia, the observed alterations in intestinal morphology were less severe than in salmonids.…”

“…These changes may widen the lamina propria and increase the presence of inflammatory cells (a mixed cell population, including lymphocytes, macrophages and polymorphonuclear leucocytes) (Baeverfjord and Krogdahl, 1996); induce enteritis in the distal intestine (Urán et al, 2008b, Urán et al, 2009and shorten villi and microvilli (van den Ingh et al, 1991).…”

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“…This has led the industry to seek alternative feed ingredients, including vegetable sources (Douglas, 2010), which is limited by the presence of anti-nutritional factors, such as a trypsin inhibitor (Urán et al, 2009). Another cost factor is the spread of diseases primarily caused by viruses and bacteria, which affect the organisms under cultivation, caused serious economic losses, company closures, and unemployment (Aguirre et al, 2000;BustilloRuiz et al, 2009;Godínez et al, 2012).…”