Diet influences the behavior, health, physiological functions, reproduction, and growth of aquatic organisms (National Research Council (NRC), 2011). While maintaining the quality of raw materials and feeds from point of origin to end use is a complex task (Patriarca and Pinto, 2017; Nogueira et al., 2020; Taroncher et al., 2021), evidences of mycotoxin contamination of feedstuffs and aquaculture feeds in recent years have been alarming, drawing increased attention worldwide (Anater et al., 2016; Gonçalves et al., 2020; Oliveira and Vasconcelos, 2020; Bashorun et al., 2023). Heightened concerns over mycotoxin contamination of feed (and food) have coincided with climate changes including higher temperatures, which are expected to favor growth of mycotoxigenic fungi leading to increased contamination of crops (both before harvest and during storage) and finished feeds (Paterson and Lima, 2010; Battilani et al., 2016; Bashorun et al., 2023).

Mycotoxins are toxic secondary metabolites produced by a diversity of fungi that contaminate agricultural crops and feeds (Zychowski et al., 2013; Marroquín-Cardona et al., 2014; Guan et al., 2023). The mycotoxin-producing fungi Aspergillus, Penicillium and Fusarium produce fumonisins (FUM), deoxynivalenol (DON), zearalenone (ZEN) and aflatoxins (AFL), all mycotoxins that are common in aquaculture feeds and that represent the greatest risks for aquaculture (Anater et al., 2016; Nogueira et al., 2020; Taroncher et al., 2021). Research reports on these mycotoxins highlight reduction of protein synthesis, modification of lipid metabolism and mitochondrial activity, and due weakening of the immune system in orally exposed animals (Wang et al., 1991; Döll et al., 2010; Tola et al., 2015; Patriarca and Pinto, 2017; Abdel-Tawwab et al., 2020; Zahran et al., 2020; Ahmed et al., 2022; Smaoui et al., 2023).

Efforts to control feed-driven mycotoxicosis in animals include management strategies that begin before crop establishment and extend to rigorous testing for mycotoxins in feed mills and adoption of mycotoxin mitigation additives for use in feeds (Boudergue et al., 2009; Zhu et al., 2016; Ahmed et al., 2022). Some of the most widely used additives for mycotoxin detoxification of feeds consist of adsorbents based on clays, micronized yeast, plant fibers, and polymers, which alleviate adverse effects of ingested mycotoxins by preventing absorption into blood and organs by complexation. One common adsorbent is bentonite, a clay with a wide variety of industrial uses (Chestnut et al., 1992; Avantaggiato et al., 2005; Hussain et al., 2017). The use of clays is a viable technical and economical solution, as they are abundantly available and can be obtained at reasonable costs. There is considerable interest in validating the efficacy of these products in aquaculture feeds, as well as evaluating the effect of different mycotoxin types on fish health (Nogueira et al., 2020; Oliveira and Vasconcelos, 2020; Smaoui et al., 2023).

In general, warm-water fish are considered more tolerant to dietary mycotoxins than cold-water counterparts, notably rainbow trout (Halver and Goldblatt, 1969; Hooft et al., 2019; Koletsi et al., 2023). However, herbivorous and omnivorous warm water fish are likely more exposed to dietary mycotoxins because are fed diets with higher levels of plant-based ingredients, especially cereal-grain by-products that usually contain higher levels of mycotoxins. In addition, species produced in tropical regions might have higher risks of exposure to mycotoxin contaminated feeds given the more suitable environmental conditions for fungal growth. Tilapia (Oreochromis spp.), particularly the Nile tilapia (O. niloticus), is one of such species largely produced in tropical and temperate regions.

Although Nile tilapia is a hardy fish in many aspects including tolerance to mycotoxins, dietary concentrations of DON/ZEN (< 0.1 to ~ 1 ppm each; Tola et al., 2015) and FUM (40 - 150 ppm; Tuan et al., 2003) have been found to adversely affect growth performance of juvenile fish. Therefore, considering the need for additional information on the potentially harmful effects of dietary mycotoxins on chronically exposed fish, the objectives of this study were to evaluate the responses of juvenile Nile tilapia to practical diets spiked with DON + ZEN or FUM and the potential beneficial effects of mycotoxin adsorbent additives.

This study followed a completely randomized design including nine dietary treatments with five replicates each ( Table 1 ). Mycotoxin-contaminated corn and mycotoxin adsorbents were sourced from Phibro Animal Health Corporation, Teaneck, NJ, USA.

In recent years, contamination of feedstuffs and aquaculture feeds with mycotoxins and their effects in farmed fish have received considerable attention (Vila-Donat et al., 2018; Gonçalves et al., 2020; Oliveira and Vasconcelos, 2020), and so have ways of attenuating their harmful effects (Olokkaran and Mathew, 2020; Zahran et al., 2020). Despite great research efforts worldwide, several aspects of mycotoxin contaminations and strategies for preventing/mitigating mycotoxicosis in farmed fish, such as upper dietary limits for different mycotoxins and effectiveness of mycotoxin mitigating additives, remain undefined for several species. Nevertheless, it is a reality that mycotoxin-contaminated diets can adversely affect the production performance and health of fish (Greeff-Laubscher et al., 2020), which is corroborated by the findings of the present study demonstrating significant reductions in final biomass and survival of Nile tilapia fed diets contaminated with sub-lethal levels of some of the most economically relevant mycotoxins, especially in the absence of adsorbent additives.

Adverse effects of dietary DON+ZEN on the performance and of Nile tilapia were observed in the present study. Accordingly, Gonçalves et al. (2018) reported decreases in growth performance of rainbow trout (Oncorhynchus mykiss) fed diets containing 1.1 and 2.7 ppm of DON for 50 days or 0.3 ppm of DON for 168 days. Döll et al. (2010) also found that dietary DON concentrations above 0.3 ppm negatively affected the performance of Atlantic salmon (Salmo salar). Hooft et al. (2019) tested the effects of DON at concentrations of 0.1, 0.7 and 1.3 ppm in diets for Nile tilapia and rainbow trout, reporting deleterious effects on trout performance at all concentrations but only at 1.3 ppm for Nile tilapia. As with other warm-water species such as channel catfish (Ictalurus punctatus; Jantrarotai and Lovell, 1990), Nile tilapia displays relatively higher tolerance to dietary mycotoxins (Tuan et al., 2002; Hooft et al., 2019) than rainbow trout (Halver and Goldblatt, 1969; Hooft et al., 2011).

Similarly to the effects of DON+ZEN, the responses of Nile tilapia fed FUM-contaminated diets in this study are in agreement with previous findings by Tuan et al. (2003), who verified negative effects in performance parameters of Nile tilapia fry fed diets containing FUM at 10 ppm. Similar effects were observed in other fish species including channel catfish (Ictalurus punctatus) and common carp (Cyprinus carpio), whereby dietary FUM at ~ 10 and 20 ppm (respectively) adversely affected performance (Lumlertdacha et al., 1995). The adverse effects of FUM in animals has been associated with alterations in sphingolipid biosynthesis. The mechanism of action seems to be linked to the enzyme N-acyltransferase which, when inhibited by FUM in the endoplasmic reticulum, leads to the toxic accumulation of free sphinganine and sphingosine in cells (Wang et al., 1991).

Adsorbents directly bind mycotoxins decreasing their absorption in the gastrointestinal tract (Huwig et al., 2001), but adsorbent efficiency varies among different adsorbing materials as well as among different mycotoxins. Inorganic and/or yeast-based mycotoxin sequestering additives show relatively lower efficiency against DON when compared to the adsorption of AFL, ZEA, and FUM (Avantaggiato et al., 2005; Kong et al., 2014; Holanda and Kim, 2021). However, even when inorganic adsorbents were tested in DON contaminated feeds, improvements in growth, feed intake, and feed efficiency were observed in pigs (Holanda and Kim, 2021), corroborating the results of this study. In addition, it is possible that a more efficient adsorption of ZEA in the DZ diets contributed to the positive effects observed in Nile tilapia in this study. Overall, our findings indicate that the adsorbents attenuated the negative effects of these mycotoxins on juvenile Nile tilapia, in agreement with findings of Zychowski et al. (2013) and Hussain et al. (2017) when a clay-based adsorbent was tested in diets contaminated with AFL-B1. The efficacy of mycotoxin adsorbents have also been demonstrated in other animals and in vitro assays, showing an overall decrease in adverse effects (Solfrizzo et al., 2001; Avantaggiato et al., 2005; Di Gregorio et al., 2014; Selim et al., 2014; Vila-Donat et al., 2018). Further studies covering economic analyses of the economic and environmental impacts of using mycotoxin adsorbents in commercial feeds are warranted.

The HSI is a somatic index commonly used to indicate differences in dietary nutrient/energy partitioning, as well as adverse effects including liver inflammation caused by mycotoxins (Mommsen, 2001). Accordingly, in this study we found a greater HSI in tilapia fed the DZ and F diets, whereas the addition of the adsorbents in both diets lowered HSI values, especially for adsorbent AC ( Table 4 ). Tuan et al. (2003) found that after eight weeks feeding Nile tilapia (2.7 g) FUM-containing diets, concentrations above 40 ppm caused substantial changes in the liver. Lumlertdacha et al. (1994) also observed altered livers in catfish after 10 weeks of exposure to dietary FUM at 20 ppm. In the present study, changes in the liver of Nile tilapia were found after 71 days of consuming the DZ (DON+ZEN = 1.6 ppm and 0.3 ppm, respectively) and F (FUM = 15 ppm) diets. However, addition of any of the adsorbents in the DZ diets prevented noticeable pathological changes in the livers based on the liver histology of Control-fed fish, indicating the effectiveness of these additives in reducing/preventing absorption of mycotoxins in the gut.

As with other animals, hematological and biochemical parameters are widely used in the evaluation of nutritional and health status, as well as adaptation to challenging environmental conditions (Fazio et al., 2013; Faggio et al., 2014; Abdel-Tawwab et al., 2015; Sehonova et al., 2018; Burgos-Aceves et al., 2019). In the present study, neither dietary mycotoxins nor adsorbents affected the assessed hematological parameters (P>0.05), but the observed differences in hematocrit indicate deleterious effects of the dietary mycotoxins. Similar observations of reduced hematocrit in Nile tilapia after receiving diets containing FUM and moniliformin for eight weeks were reported by Tuan et al. (2003). Abdel-Tawwab et al. (2020) also reported decreased hematocrit values in European sea bass (Dicentrarchus labrax) fed diets with ZEN. The mycotoxin toxicity might have induced a hypochromic macrocytic anemia, which inhibits red blood cell enlargement (Abdel-Tawwab et al., 2020). Other parameters, such as BUN analysis, are mainly associated with gill and liver diseases (Stoskopf, 1993), but there were no statistical differences between the treatments in this experiment.

In the present study, the dietary concentrations of mycotoxins were well above those reported for commercial feeds for both DON+ZEN and FUM. Pietsch et al. (2014) reported a wide variation of DON (0.066 to 0.825 ppm) and ZEN (0.003 to 0.051 ppm), and ~3.42 ppm of FUM in commercial feeds. Therefore, our study not only highlight the deleterious effects of the evaluated mycotoxins, but also demonstrate the potential benefits of using commercially available additives for prevention of potential mycotoxicosis. In addition, adverse effects arising from chronic exposure to relatively lower levels of dietary mycotoxin may also occur as aspects such as health status, environmental conditions, and exposure period to contaminated feeds may influence the fish’s responses to the toxins (Gonçalves et al., 2020; Oliveira and Vasconcelos, 2020).

In summary, exposure of juvenile Nile tilapia to dietary DON+ZEN and FUM at 1.6 + 0.3 ppm and 15 ppm, respectively, during a 71-day period adversely affects production performance and survival of the fish. Inclusion of adsorbent additives in the diets may help in attenuating/preventing adverse effects driven by mycotoxin contamination.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The animal study was approved by School of Fisheries, Aquaculture, and Aquatic Science, Auburn University, complying with regulations on the use of animals (approval code 20183337). The study was conducted in accordance with the local legislation and institutional requirements.

DF: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Project administration, Resources, Software, Writing – original draft, Writing – review & editing. SP: Conceptualization, Data curation, Formal Analysis, Methodology, Writing – review & editing. SK: Conceptualization, Formal Analysis, Investigation, Writing – review & editing. SB: Conceptualization, Data curation, Investigation, Methodology, Writing – review & editing. WR: Conceptualization, Methodology, Writing – review & editing. DN: Funding acquisition, Methodology, Resources, Supervision, Writing – review & editing. DD: Conceptualization, Data curation, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing.