Over recent years several factors led to an escalation of fishmeal prices. As an alternative to fishmeal there is a trend to increase the levels of cheaper plant protein sources in aquaculture feeds. As a result of this trend, aquaculture feeds have a higher risk of being contaminated with one or more types of mycotoxins. The increasing mycotoxin contamination of crops represents a widespread problem in the animal feed industry.
In general, the effects of mycotoxins are associated with reduced growth and health status of fish and other farmed animals. In terrestrial animals the toxic effects of mycotoxins are well known and can be of different nature such as carcinogenic (e.g. aflatoxin B1, ochratoxin A, fumonisin B1), estrogenic (zearalenone), neurotoxic (fumonisin B1), nephrotoxic (ochratoxin), dermatoxic (trichothecenes) or immunosuppressive (aflatoxin B1, ochratoxin A and T-2 toxin).
Despite the limited number of studies on the effect of mycotoxins on aquaculture species, there is increasing evidence that mycotoxins can cause several pathologies and growth problems in different fish and shrimp species. Recently Tu et al, (2010), showed that diets contaminated with aflatoxin concentrations of 50 g AFB1/kg feed induced a significant (P<0.05) reduction in weight gain in Tra catfish (Pangasionodon hypophtalmus). Moreover, fish fed diets with 50, 100 and 250 g AFB1/kg feed exhibited higher alanine aminotransferase and aspartate aminotransferase, which suggests the occurrence of liver damage. Disease resistance was compromise in fish fed AFB1 contaminated diets and exposed to Edwardsiela ictaluri. In another study with tilapia (O. niloticus x O. aureus), Deng et al. (2010), concluded that, despite evidence that tilapia is relatively more tolerant to AFB1 than other species, fish fed diets containing 245 g AFB1 / kg for more than 20 weeks exhibited impaired growth and hepatic disorders.
For ochratoxin A, Manning et al (2003) reported a reduction in body weight gain of channel catfish fed diets with 2 ppm of ochratoxin A for two weeks and 1 ppm for 8 weeks. Reduced FCR was also observed in the same species with contamination levels of 4 and 8 ppm. In rainbow trout pathological signs of ochratoxicosis included liver necrosis, pale, swollen kidneys and high mortality (Hendricks, 1994).
Long-term exposure effects of FB1 were reported in carp by Pepeljnjak et al (2002). These authors showed that exposure to 0.5 and 5.0 mg per kg body weight is not lethal to young carp, but can produce adverse physiological effects with kidney and liver being the key target organs for the fumonisin B1 action. In channel catfish, dietary levels of fumonisin B1 of 20 ppm or above have been shown to result in lower weight gain and significant decrease in hematocrit and red and white blood cells than those fed lower doses (Lumlertdacha et al., 1995). However in another study, minimal adverse effects have been reported in channel catfish fed F. moniliforme culture material containing 313 ppm of fumonisin B1 for 5 weeks (Brown, et al., 1994).
A recent study, Hooft et al (2010) observed that weight gain, feed intake and feed efficiency (FE, gain:feed) of trout decreased significantly (p<0.05) with increasing levels of deoxynivalenol (DON) in the diets starting at levels of 0.5 ppm. Significant histopathological changes in liver and intestine with increasing dietary levels of DON were also reported. In Atlantic salmon diets with 3.7 mg/kg of DON resulted in 20 per cent reduction in feed intake, 18 per cent increase in FCR and 31 per cent reduction in specific growth rate (Dll et al., 2010).
As there are serious impacts of mycotoxins in fish, it is of extreme importance that the levels of mycotoxins in feed ingredients used are known.
Every year BIOMIN conducts a mycotoxin survey to get an overview on contamination of the agricultural commodities in different regions worldwide. Between the period of January and December 2010 a total of 369 samples were analyzed in South-East Asia for the most important mycotoxins in terms of agriculture and animal production aflatoxins (Afla), zearalenone (ZON), deoxynivalenol (DON), fumonisins (FUM) and ochratoxin A (OTA).
The analyses were performed at ROMER Labs Singapore Pte Ltd (Singapore) and all samples were analysed by HPLC. For the purpose of data analysis, nondetection levels were based on the quantification limits of the test method for each mycotoxin - Afla (4 ppb), ZON (32 ppb), DON (50 ppb), FUM (100 ppb), OTA (2 ppb).
From all surveyed samples in South-East Asia which includes Malaysia, Philippines, Thailand, Vietnam, Indonesia, 65 per cent, 49 per cent, 41 per cent, 57 per cent and 32 per cent tested positive for contamination of Afla, ZON, DON, FUM and OTA respectively (Table 1). Afla was present at an average level of 22 ppb and FUM and ZON were present at an average of 493 ppb and 55 ppb, respectively.
Table 1 - Occurrence of mycotoxins in South-East Asia
|Number of tests||369||369||369||369||369|
|Percentage of positive (%)||65||49||41||57||32|