Atlantic salmon (Salmo salar L.) parr fed genetically modified soybeans and maize: Histological, digestive, metabolic, and immunological investigations.

Physiological and health related responses to dietary inclusion of genetically modified (GM) full-fat soybean meal (Roundup Ready; GM-soy) and maize (MON810 Bt-maize; GM-maize), as well as non-parental, untransformed lines (nGM-soy and nGM-maize D2), were evaluated in farmed Atlantic salmon (Salmo salar L.) parr during the first 8 months of feeding. Significant effects of dietary GM presence were only found in intestinal Na+-dependent d-glucose uptake and SGLT1 protein level in the region pyloric caeca in which the highest values were found in the GM-soy, intermediate in the nGM-soy, and lowest in the standard FM fed groups. Data from this study confirm that GM soybeans (RRS) and maize (MON810) at inclusion levels of about 6% appear to be as safe as commercially available nGM soy and maize in diets for Atlantic salmon parr. Results from studies with higher inclusion levels and with non-modified, isogenic or near-isogenic parental lines as control groups are pending.

Histological, digestive, metabolic, hormonal and some immune factor responses in Atlantic salmon, Salmo salar L., fed genetically modified soybeans.

The paper reports the second and final part of an experiment aiming to study physiological and health-related effects of genetically modified (GM) soybean meal (SBM) type Roundup Ready soybean (RRS) in diets for post-smolt Atlantic salmon. For 3 months salmon were fed diets containing 172 g kg(-1) full-fat SBM from RRS (GM-soy) or an unmodified, non-isogenic line (nGM-soy), or a reference diet with fishmeal as the sole protein source (FM). Slight differences in anti-nutrient levels were observed between the GM and nGM-soy. Histological changes were observed only in the distal intestine of the soy-fed fish. The incidence of moderate inflammation was higher in the GM-soy group (9 of 10 sampled fish) compared with the nGM-soy group (7 of 10). However, no differences in the concomitant decreases in activities of digestive enzymes located in the brush border (leucine aminopeptidase and maltase) and apical cytoplasm (acid phosphatase) of enterocytes or in the number of major histocompatibility complex class II+ cells, lysozyme activity, or total IgM of the distal intestine were observed. GM compared with nGM-soy fed fish had higher head kidney lysozyme (11,856 vs. 10,456 units g(-1) tissue) and a tendency towards higher acid phosphatase (0.45 vs. 0.39 micromol h(-1) kg(-1) body mass in whole tissue) activities, respectively. Plasma insulin and thyroxin levels, and hepatic fructose-1,6-bisphosphatase and ethoxyresorufin-O-deethylase activities were not significantly affected. It is not possible, however, to conclude whether the differences in responses to GM-soy were due to the genetic modification or to differences in soy cultivars in the soy-containing diets. Results from studies using non-modified, parental line soybeans as the control group are necessary to evaluate whether genetic modification of soybeans in diets poses any risk to farmed Atlantic salmon.

Response to soy: T-cell-like reactivity in the intestine of Atlantic salmon, Salmo salar L.

T-cell-mediated hypersensitivity could be central in soybean meal (SBM)-induced intestinal changes in salmon. However, tools for immunohistochemical detection of T cells have been lacking in teleosts, including Atlantic salmon. Application of a specific histochemical protocol allowed demonstration of T-cell-like reactivities in formalin-fixed, paraffin-embedded tissues using an antibody reacting to a conserved region of human CD3epsilon (Dako A0452). Characteristic staining was observed in cells of the thymus as well as distal intestine, skin, gills and spleen. These cells were negative for immunoglobulin M (IgM). Intestinal intraepithelial leucocytes were CD3epsilon positive. During the SBM-induced enteropathy, the mixed inflammatory infiltrate in the lamina propria of the distal intestine included many lymphocytes with a T-cell-like reactivity. Real-time polymerase chain reaction revealed significantly increased expression of a complex polypeptide (CD3pp), CD4 and CD8beta (P < 0.05) in the distal intestine of SBM-fed fish compared to fish meal-fed reference fish. Increased reactivity for extracellular IgM in the lamina propria and a positive material between the epithelial cells at the tips of the folds was observed, possibly due to leakage of IgM through an abrogated epithelial barrier. In conclusion, a T-cell-like response appears to be involved in this example of a food-sensitive enteropathy.

An examination of the intestinal tract of Atlantic salmon, Salmo salar L., parr fed different varieties of soy and maize.

This study was conducted to investigate the long-term effects of feeding plant products from both traditional breeding and from biotechnology on intestinal somatic indices, histology and cell proliferation in first-feeding Atlantic salmon, Salmo salar L. (initial weight 0.21 +/- 0.02 g). A standard fishmeal diet (standard fishmeal) was formulated to contain fishmeal as the sole protein source and suprex maize as the main starch source. Six experimental diets were then developed: two in which some of the fishmeal was replaced with commercially available, genetically modified Roundup Ready full-fat soybean meal (GM-soy) or commercially available, non-GM full-fat soybean meal (nGM-soy) at a level of 12.5% of the total diet, and four diets in which the suprex maize was replaced with two lines of GM-maize (Dekalb 1; D1 and Pioneer 1; P1), both products of event MON810, and their half-sibling non-GM counterparts (Dekalb 2; D2 and Pioneer 2; P2), at a level of 12.1% of total diet. Each diet was fed to fish in triplicate tanks and the experiment lasted for 8 months, during which the fish reached a final weight of 101-116 g. There was no significant effect of diet on the intestinal indices, nor were histological changes observed in the pyloric caeca or mid intestine. In the distal intestine, one of nine sampled fish fed nGM-soy showed moderate changes, two of nine sampled fish fed GM-soy showed changes, one with moderate and one with severe changes, and two of nine fish fed nGM-maize D2 had moderate changes. Using a monoclonal antibody against proliferating cell nuclear antigen (PCNA), cell proliferative responses to the experimental diets were assessed. In fish fed both soy diets, a significantly higher (P < 0.05) cell proliferation response was observed in the distal intestine concomitant with an increased localization of PCNA positive cells along the whole distal intestinal folds. The PCNA response among the nGM-soy group was significantly higher compared with all the other diet groups. In contrast, for fish exposed to dietary maize (type D) compared with fish fed the standard fishmeal, the soy-diets (GM-soy and nGM-soy) and maize (type P), a significantly lower (P < 0.05) cell proliferation response was observed in the distal intestine. Results indicated that the GM plant products investigated in this study, at about 12% inclusion level, were as safe as commercially available non-GM products, at least in terms of their effect on indices and histological parameters of the Atlantic salmon intestinal tract.

Effects of soybean meal and salinity on intestinal transport of nutrients in Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss).

Groups of fresh- and seawater-adapted Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss) were fed diets with (SBM diet) or without (control diet) extracted soybean meal (30% of protein substituted with SBM) for 3 weeks. Average fish size per group ranged from 597 to 1763 g. One tank or net pen per species, dietary group and water salinity was used. In vitro nutrient transport (D-glucose, the L-amino acids aspartate, lysine, methionine, phenylalanine and proline, and the dipeptide glycyl-sarcosine) was measured using intact tissue (everted sleeve method) from the different postgastric intestinal regions. The dimensions of the different intestinal regions were also measured for each treatment group. Results indicate that SBM causes decreased carrier-mediated transport and increased permeability of distal intestinal epithelium for the nutrients, and the capacity of this region to absorb nutrient was diminished. Salinity may also affect the relative contribution of carrier-mediated and independent uptake to total nutrient absorption.

The intestines of carnivorous fish: structure and functions and the relations with diet.

The intestine is a complex multifunctional organ. In addition to digesting and absorbing feedstuffs, the intestine is critical for water and electrolyte balance, endocrine regulation of digestion and metabolism, and immunity. The intestines of carnivorous fish have evolved for processing a highly digestible, nutrient dense diet that is high in protein and low in carbohydrate. Correspondingly, abilities to digest protein are well developed, but carbohydrate digestion is low compared to omnivorous and herbivorous fish. Furthermore, the evolutionary stable diet is associated with a lack or reduced abilities to adaptively modulate digestive functions to match changes in diet composition. Despite similar selective pressures, intestinal structure is highly variable among carnivorous fish, reflecting phylogenetic diversity. Due to economic considerations, diets for cultured species often have varying proportions of plant-based ingredients. Although such feeds are effective for raising omnivorous and herbivorous species, they have provided limited success for carnivores, and this has been attributed to digestive limitations. Recent evidence of inflammatory responses to as yet unidentified components of some plants suggest involvement of the enteric immune system. Changes in temperature and salinity alter intestinal structure and functions, and therefore processing of dietary inputs. A relatively unknown component of the intestine involves the resident microbiota and its role in the health and disease of carnivoraus fish.