Food Safety: The Risk of Mycotoxin Contamination in Fish

Mycotoxins are commonly found in animal feeds, and fish feeds are no exception to this. The need to feed fish in aquaculture with compounded feeds leads to the increasing inclusion of plant-derived feed ingredients that have a higher probability of containing mycotoxins. Since fish appear to be quite sensitive to mycotoxins, further research on mycotoxin toxicity in fish is recommended. Depending on the chemical characteristics of an individual mycotoxin and the biotransformation abilities of the different fish species, certain mycotoxins can could be found in the edible parts of a fish. Thus, the consumption of fish products increases the potential risk of mycotoxin exposure for humans. This chapter reviews the risks associated with different groups of mycotoxins and makes recommendations on how to minimize these risks in the future

Zearalenone (ZEN) and its influence on regulation of gene expression in carp (Cyprinus carpio L.) liver tissue

Zearalenone (ZEN) is a frequently-occurring mycotoxin in both animal and fish feeds. In order to characterize its effects on carp, three groups of fish were fed for 28 days with feeds contaminated with three different levels of ZEN (low: 332 µg kg(-1), medium: 621 µg kg(-1), and high: 797 µg kg(-1) feed). The reversibility of the effects of ZEN was assessed by feeding all of the groups with uncontaminated feed for a further 14 days. Gene expression of immune genes in the liver tissue of the fish was analysed, revealing reduced expressions of immune, antioxidative, and estrogen-related genes after the fish had been exposed to ZEN. However, the expression of vacuole-type H⁺ ATPase increased substantially with ZEN exposure, thus supporting the previously-reported sensitivity of lysosomal functions to ZEN. Feeding the fish with a ZEN-free diet for a further two weeks changed the effects of ZEN on the expression of some genes, including the expressions of the cytokines IL-1β, IL-8, IL-10, and arginase 2, which were not influenced after four weeks of treatment, but showed lower values after the recovery phase in fish previously treated with ZEN compared with the control group. In summary, this study confirmed the broad effects of ZEN on different essential functions in carp and suggests that the current maximum allowable levels in compound feed are too high to prevent damage to fish

Distress regulates different pathways in the brain of common carp: an initial study

For the present study, a stress trial with common carp, which is one of the most important species in aquaculture world-wide, was conducted to identify relevant gene regulation pathways in different areas of the brain. Acute distress by air exposure significantly activated the expression of the immediate early gene c-fos in the telencephalon. In addition, evidence for regulation of the two crf genes in relation to their binding protein (crh-bp) have been highlighted in this initial study. Inference about the effects of distress by air exposure has been obtained by using point estimation which allows the prediction of a single value that is the best description of the up to know mostly unknown effects of stress in different brain regions of carp. Furthermore, principal component analyses have been performed to reveal possible regulation patterns in the different parts of the fish brain. In conclusion, these initial studies on gene regulation in the carp brain influenced by exposure to a stressor reveal that a number of genes may be successfully used as markers for exposure to unfavourable conditions

Ethoxyquin : a feed additive that poses a risk for aquatic life

Ethoxyquin (EQ) is an antioxidant that has, to date, been commonly used in feed production. Reports on the detrimental effects of this substance on vertebrates are growing, but effects in aquatic systems have rarely been described. Therefore, the present study was conducted using serial concentrations of EQ ranging from 0.03 to 16.5 mg l-1 to determine effects on 3 types of aquatic organisms. In zebrafish, 5 mg l-1 EQ caused mortality (25%) and a further 62.5% of the embryos showed yolk sac edema as well as deformed bodies or missing eyes. Furthermore, all the investigated EQ concentrations decreased the heart rate of the embryos. The lowest observed effect level was 0.31 mg l-1. In addition to zebrafish, the study also used water fleas Daphnia magna and green algae (Scenedesmus obliquus and Chlorella vulgaris). These treatments revealed that daphnids are also sensitive to EQ, exhibiting detrimental effects with a half-maximal effective concentration (EC50) of 2.65 mg l-1 after 48 h of exposure. The algae appeared to be at least 2 times less sensitive to EQ than fish embryos or daphnids. The results were used to calculate the risk for aquatic life resulting in a maximum tolerable level of 1 µg l-1 for fish embryos and daphnids, with a safety factor of 300. According to current knowledge, this does not exceed environmental concentrations of this substance. However, this study raises further concern about the (until recently) legal maximum tolerable EQ levels in fish feeding and the rather slow pace at which authorization to use EQ as a feed additive for diverse animals in Europe is being suspended

Risk assessment for mycotoxin contamination in fish feeds in Europe

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)Mycotoxins are difficult to monitor continuously, and a tool to assess the risk would help to judge if there is a particular risk due to the inclusion of certain feed ingredients. For this, the toxin contents of 97 commercial fish feeds have been estimated, and the most prominent toxins in fish feed are calculated to be deoxynivalenol, zearalenone, fumonisins and enniatins. These pose a risk to fish well-being, as can be calculated by the Bayesian models for determining the critical concentrations 5% (CC5) for the different toxins. Besides fishmeal, wheat, soybean products and corn are regularly used as fish feed ingredients. The calculated scenarios show that fish are at high risk of toxin contamination if feed ingredients of low quality are chosen for feed production. Due to this, specific maximum allowable levels for several mycotoxins in fish feeds should be established

Toxicity of ochratoxin to early life stages of zebrafish (Danio rerio)

Ochratoxin A (OTA) is a known contaminant in fish feed but its effect on fish health remains rather unknown. A study was conducted to investigate the effects of different concentrations of ochratoxin on early life stages of zebrafish (Danio rerio). The tests with ochratoxin A showed a correlation between the exposure to mycotoxin and the amount of damage. The mortality rate and the incidents of embryonal damage was increased by increasing ochratoxin concentrations. The calculations resulted in a lethal concentration for 50% of the embryos (LC50) of 0.29 mg/L and a concentration at which 50% of the animals showed impairment (EC50) of 0.36 mg/L after 96 h of exposure. During the test, reduced heart rates were also observed revealing a clear dose-response relationship. The EC50 determination for this endpoint was 1.26 mg/L after 72 h of exposure. The measurement of oxidative stress was proven to be the most sensitive system to indicate OTA effects on the zebrafish embryos with an EC50 value of 0.067 mg/L after 72 h of exposure. The test validity was given because the control test with 3,4-Dichloroaniline (3,4-D) showed a LC50 value of 2.88 mg after 96 h of exposure which is comparable to the available reference values. According to the current knowledge, these experimental doses did not exceed the environmental concentrations of this ochratoxin A. However, this study raises concerns about the effects of ochratoxin on fish

Physiological responses of carp (Cyprinus carpio L.) to dietary exposure to zearalenone (ZEN)

Zearalenone (ZEN) is a frequent contaminant of animal feeds, but systemic effects on fish and possible metabolic costs have not yet been investigated. In order to fill this gap a feeding trial with juvenile carp was conducted. The fish were fed ZEN-contaminated diets at three concentrations (low: 332 μg kg−1, medium: 621 μg kg−1, and high: 797 μg kg−1 final feed, respectively) for four weeks. Possible reversible effects of ZEN were evaluated by feeding an additional group with the mycotoxin for four weeks period and the  uncontaminated diet for further two weeks. After that possible ZEN effects on enzyme activities in kidney, spleen, liver and muscle tissue were investigated to get an organism-wide aspect of ZEN effects. Most organs appeared to (over)compensate ZEN effects during the exposure to this mycotoxin, which caused metabolic costs. Oxygen consumption increased in fish treated with the two higher ZEN concentrations via the diet. The differences between the treatments persisted also after the recovery phase of two weeks. Thus, the present study provided evidence of effects of ZEN on carbohydrate metabolism, lipid peroxidation in organs and metabolic oxygen demand. This is the first evidence for increased metabolic costs in a fish species due to exposure to the mycotoxin ZEN

Occurrence of Fungi and Fungal Toxins in Fish Feed during Storage

Periods of unfavorable storing conditions can lead to changes in the quality of fish feeds, as well as the development of relevant mycotoxins. In the present study, a commercial fish feed was stored under defined conditions for four weeks. The main findings indicate that even storing fish feeds under unsuitable conditions for a short duration leads to a deterioration in quality. Mycotoxin and fungal contamination were subsequently analyzed. These investigations confirmed that different storage conditions can influence the presence of fungi and mycotoxins on fish feed. Notably, ochratoxin A (OTA) was found in samples after warm (25 °C) and humid (>60% relative humidity) treatment. This confirms the importance of this compound as a typical contaminant of fish feed and reveals how fast this mycotoxin can be formed in fish feed during storage

Organ damage and hepatic lipid accumulation in carp (Cyprinus carpio L.) after feed-borne exposure to the mycotoxin Deoxynivalenol (DON)

Deoxynivalenol (DON) frequently contaminates animal feed, including fish feedused in aquaculture. This study intends to further investigate the effects of DON on carp(Cyprinus carpio L.) at concentrations representative for commercial fish feeds.Experimental feeding with 352, 619 or 953 μg DON kg−1 feed resulted in unaltered growthperformance of fish during six weeks of experimentation, but increased lipid peroxidationwas observed in liver, head kidney and spleen after feeding of fish with the highest DONconcentration. These effects of DON were mostly reversible by two weeks of feeding theuncontaminated control diet. Histopathological scoring revealed increased liver damage inDON-treated fish, which persisted even after the recovery phase. At the highest DONconcentration, significantly more fat, and consequently, increased energy content, wasfound in whole fish body homogenates. This suggests that DON affects nutrientmetabolism in carp. Changes of lactate dehydrogenase (LDH) activity in kidneys andmuscle and high lactate levels in serum indicate an effect of DON on anaerobicmetabolism. Serum albumin was reduced by feeding the medium and a high dosage ofDON, probably due to the ribotoxic action of DON. Thus, the present study providesevidence of the effects of DON on liver function and metabolism

Cytotoxic effects of pentachlorophenol (PCP) and its metabolite tetrachlorohydroquinone (TCHQ) on liver cells are modulated by antioxidants

The worldwide distribution and high bioaccumulation potential of pentachlorophenol (PCP) in aquatic organisms imply a high toxicological impact in aquatic systems. Firstly, our investigations show that, similar to mammalian cell lines, PCP can be metabolized to tetrachlorohydroquinone (TCHQ) in the permanent cell line derived from rainbow trout liver cells (RTL-W1). Moreover, we demonstrate that PCP as well as its metabolite TCHQ is capable of influencing the viability of these cells. Three cell viability assays were performed to assess possible cellular targets of these substances. Thus, the cytotoxicity of the PCP-derivative TCHQ was shown for the first time in a fish cell line. Further investigations revealed the involvement of ROS in the cytotoxicity of PCP and its metabolite TCHQ. The observation of oxidative stress provides a plausible explanation for the increased cytotoxicity at higher concentrations especially for PCP and implies possible mechanisms underlying these observations. In addition, antioxidants such as ascorbic acid and quercetin modulate the detrimental effects of PCP and TCHQ whereby both compounds exacerbate the cytotoxic effects of high PCP and TCHQ concentrations