This study investigated in rainbow trout (Oncorhynchus mykiss) if diet composition and feeding level affect faecal bile acid loss, and whether this reflects on the apparent digestibility coefficient (ADC) of fat. Six diets were formulated with either fishmeal or plant protein as main protein source. This created a contrast in the supply of bile acids, the bile acid precursor cholesterol, taurine and the taurine precursors (methionine + cysteine) involved in bile acid conjugation. For both protein sources, three diets were formulated with increasing inclusion of a non-starch polysaccharide (NSP)-rich ingredient mixture (0.0, 82.0 and 164.2 g/kg diet). This aimed at enhancing faecal bile acid loss. Fish were fed both restrictively (1.2% BW/day) and to satiation.A similar fat ADC was found when substituting fishmeal with a plant protein mixture, suggesting that the lower content of bile acids, cholesterol, taurine, methionine and cysteine in the plant-based diets did not limit fat digestion. Faecal bile acid loss increased alongside dietary NSP level, however, only during satiation feeding and most strongly for fish fed the fishmeal-based diets. Enhanced faecal bile acid loss was not caused by NSP-bile acid binding/entrapment, but by an increase in faeces production. During satiation feeding, fat ADC negatively correlated with faecal bile acid loss.From this it is concluded that bile acid availability/synthesis can become limiting for fat digestion in rainbow trout under conditions that enhance faecal bile acid loss (i.e. dietary NSP level and feeding level). K E Y W O R D Sbile acids, cholesterol, fat digestibility, non-starch polysaccharides, Oncorhynchus mykiss, taurine | 1171 STAESSEN ET Al.

The first part of this study evaluates the occurrence of mycotoxin patterns in feedstuffs and fish feeds. Results were extrapolated from a large data pool derived from wheat (n = 857), corn (n = 725), soybean meal (n = 139) and fish feed (n = 44) samples in European countries and based on sample analyses by liquid chromatography/tandem mass spectrometry (LC-MS/MS) in the period between 2012–2019. Deoxynivalenol (DON) was readily present in corn (in 47% of the samples) > wheat (41%) > soybean meal (11%), and in aquafeeds (48%). Co-occurrence of mycotoxins was frequently observed in feedstuffs and aquafeed samples. For example, in corn, multi-mycotoxin occurrence was investigated by Spearman’s correlations and odd ratios, and both showed co-occurrence of DON with its acetylated forms (3-AcDON, 15-AcDON) as well as with zearalenone (ZEN). The second part of this study summarizes the existing knowledge on the effects of DON on farmed fish species and evaluates the risk of DON exposure in fish, based on data from in vivo studies. A meta-analytical approach aimed to estimate to which extent DON affects feed intake and growth performance in fish. Corn was identified as the ingredient with the highest risk of contamination with DON and its acetylated forms, which often cannot be detected by commonly used rapid detection methods in feed mills. Periodical state-of-the-art mycotoxin analyses are essential to detect the full spectrum of mycotoxins in fish feeds aimed to prevent detrimental effects on farmed fish and subsequent economic losses for fish farmers. Because levels below the stated regulatory limits can reduce feed intake and growth performance, our results show that the risk of DON contamination is underestimated in the aquaculture industry.

This study assessed whether the toxicological effects of deoxynivalenol (DON) produced by Fusarium graminearum in rainbow trout (Oncorhynchus mykiss) are altered by the co-exposure to a mixture of toxins produced by Fusarium verticillioides (FUmix). This FUmix contained fusaric acid and fumonisin B1, B2 and B3. Four diets were formulated according to a 2 × 2 factorial design: CON-CON; CON-FUmix; DON-CON; and DON-FUmix. Diets with and without DON contained on average 2700 and 0 µg/kg feed, respectively. The sum of the analysed FUmix toxins was 12,700 and 100 µg/kg feed in the diets with and without FUmix, respectively. The experiment consisted of a 6-week restrictive feeding period immediately followed by a 2-week ad libitum feeding period. Growth performance measurements were taken per feeding period. Histopathological measurements in the liver and gastrointestinal tract (pyloric caeca, midgut and hindgut) were assessed at the end of week 1 and week 6 of the restrictive feeding period and at week 8, the last day of the ad libitum feeding period. During both restrictive and ad libitum feeding, the effects of FUmix and DON on growth performance were additive (no interaction effect; p > 0.05). During the restrictive feeding period, exposure to DON (p ≤ 0.001) and FUmix (p ≤ 0.01) inhibited growth and increased feed conversion ratio (FCR). During this period, DON exposure decreased the protein (p ≤ 0.001) and energy retention (p ≤ 0.05) in the trout. During the ad libitum feeding period, FUmix affected HSI (p ≤ 0.01), while DON exposure reduced feed intake (p ≤ 0.001) and growth (p ≤ 0.001) and increased FCR (p ≤ 0.01). In general, for both liver and intestinal tissue measurements, no interaction effects between DON and FUmix were observed. In the liver, histopathological analysis revealed mild alterations, increased necrosis score by DON (p ≤ 0.01), increased glycogen vacuolization by FUmix (p ≤ 0.05) and decreased percentage of pleomorphic nuclei by FUmix (p ≤ 0.01). DON had a minor impact on the intestinal histological measurements. Over time, some of the liver (glycogen vacuolization score, pleomorphic nuclei; p ≤ 0.01) and intestinal measurements (mucosal fold and enterocyte width; p ≤ 0.01) were aggravated in fish fed the FUmix contaminated diets, with the most severe alterations being noted at week 8. Overall, the co-exposure to FUmix and DON gave rise to additive effects but showed no synergistic or antagonistic effects for the combination of DON with other Fusarium mycotoxins.

In the following decade, several experimental studies were carried out that recognised the sensitivity of rainbow 13 Climate changeGlobally, climate change is manifested especially through elevated average yearly temperatures, increased CO2 levels and extreme weather conditions (drought or flood). These manifestations are all expected to affect the growth patterns of fungi and therefore the production of mycotoxins (Medina et al., 2017). This realization has led to concerns about upcoming food and feed security, and led to predictive models estimating the impact of climate change on mycotoxin production in cereals, in Europe (Van der . By the year 2040, DON contamination in wheat is expected to increase mainly in North-Western Europe, in some regions increased levels may be up to 3-fold compared to the original concentrations (van der Fels-Klerx et al., 2012a). Within the next 100 years, in a scenario of a 2 °C elevated temperature, the risk of aflatoxin B1 (AFB1) contamination in corn will increase mainly in Southern regions of Europe such as Spain, Italy and the Balkans because of optimal growth conditions for Aspergillus flavus (Battilani et al., 2016). In general, as a consequence of climate change Europe may witness an extension of AFB1 distribution from tropical to previously considered temperate areas, and a similar extension of Fusarium graminearum from Southern to Central and Northern Europe (Moretti et al., 2019). For instance, in the Netherlands, the main strain of Fusarium fungi in wheat always had been F. culmorum, but after the year 2000, F. graminearum became more dominant (Waalwijk et al., 2003). In Luxembourg, a shift from F. graminearum to F. culmorum and vice versa has been reported, indicating plasticity of Fusarium strains (Beyer et al., 2014). Overall, although exact proliferations under field conditions remain unpredictable, these studies provide several different examples confirming that in times of climate change, Europe should expect an increased presence and distribution of fungi on cereals and other crops, and the associated risk of contaminations with mycotoxins. Globalization of the tradeThe globalization of trade is leading to encountering unpredictable mycotoxin patterns in imported agricultural commodities, including aquafeed (Binder et al., 2007). For the relatively cold and wet parts of Northern Europe, trade globalization increases the risk of mycotoxins, simply because aflatoxin B1 is produced by Aspergillus fungi which thrive in warm and dry climate areas. One such example for the agricultural sector occurred in the Netherlands in 2013 (Focker et al., 2021) when aflatoxin M1 was discovered in cow milk, linked to aflatoxin B1contaminated maize imported from Eastern Europe and included in the feed of the animals consumed. Although a similar clear example has not been reported for aquaculture, the aquafeed sector certainly is aware of increased risks (Gonçalves et al., 2020a). For example, in Europe, increased risks exist for soybean, with soybean meal as a typical example of an...