Adapt to pivot in Asian aquaculture

Knowing the hidden threat of mycotoxins in aquafeeds and tools to assess functional ingredients improves production efficiency

In November 2022, DSM Animal Nutrition Asia Pacific organised its 27th DSM Aqua Conference as an in-person meeting in Bangkok, Thailand. The theme was “Adapt to Pivot”.

The program had six presentations from industry experts discussing some of the hot topics faced by the industry. The report in issue January/February (page 43-46), covered four of these. In this issue, we continue this conference report with two presentations covering mycotoxins in aquaculture and tools to assess functional ingredients.

Mycotoxins in aquaculture

Dr Rui A. Gonçalves has studied the occurrences of mycotoxins in plant meals used in aquafeeds and in his presentation titled, “Mycotoxins in Asian aquaculture: A hidden threat in Southeast Asian aquaculture”, he provided some data on occurrences of mycotoxins, mainly aflatoxin (AF), zearalenone (ZEN), deoxynivalenol (DON), fumonisins (FUM), ochratoxin A (OTA) and trichothecenes (T-2). Mycotoxins in ingredients and finished feeds have been surveyed on a yearly basis since 2020 (see pages 50-53).

The contamination chain is from crops and grains to feeds; from harvesting to distribution, it moves along the transportation process and storage in the feedmill. High water activity plays a big role in mycotoxin contamination in grains and mycotoxins at harvest will be transferred into feeds. Storage mycotoxins are derived from Aspergillus spp and Penicillin spp.

Gonçalves explained the results of the 2015 survey of 2,176 samples of plant meals used for aquafeeds in Southeast Asia and pointed out that cottonseed meal is well known to have high levels of aflatoxin (~2,500µg/kg or ppb), corn gluten meal had high levels of deoxynivalenol and fumonisins at more than 2,000ppb while wheat bran had around 1,660ppb of deoxynivalenol . Most fungi can produce more than one mycotoxin and the co-occurrence of mycotoxins was demonstrated in a 2016 survey covering 18 mycotoxins.

“Only a few meals, wheat flour and soybean cake, were contaminated with only one mycotoxin. Many others have co-occurrence of 2-6 mycotoxins such as wheat bran with zearalenone, deoxynivalenol and fumonisins. There was co-occurrence of 7-8 mycotoxins in corn dust, cotton gluten and DDGS,” said Gonçalves.

A survey in 2021-2022 showed mycotoxin occurrences specific to the Asian region. Deoxynivalenol contamination was high in 15 samples of cotton seed meal at 1,410ppb. The mean value for fumonisins in 60 corn samples was 1,373ppb but the highest level was as high as 9,000ppb. The contamination of fumonisins was also high in finished feed at 498ppb.

A hidden threat?

The answer is “maybe”. In Asian aquaculture there are almost 424 cultured species, according to FAO data. The results on contamination in plant meals used in aquafeeds (fish and shrimp feeds) were compared to data available in published literature on contamination levels affecting rainbow trout, pacific white shrimp, carp and red tilapia in the case of deoxynivalenol. In Asian aquafeeds, aflatoxin contamination was close to 221ppb while contamination by fumonisins was up to 573ppb. Published research on mycotoxin contamination in Pacific white shrimp, black tiger shrimp, rainbow trout, Nile tilapia and carp showed contamination of aflatoxin to be as high as 2,500ppb in Nile tilapia and black tiger shrimp and with fumonisins at 5000ppb in carp and 150ppb in Nile tilapia fingerlings.

“Factors such as age, as well as nutritional and health status, rearing density and environmental conditions of animal tested influenced outcome of trials leading to variable sensitivity. It is difficult to estimate the risk that these concentrations have on aquaculture species, as most published studies investigating the effect of mycotoxins in aquaculture species tested contamination at unrealistically high levels to be present in aquafeeds. For industry use, it does not make any sense,” said Gonçalves.

“In risk mitigation, steps should be consciously taken based on indicators, to counter, in advance, the effects of mycotoxins in the aquaculture industry. One size-fits all solutions is not advisable.”

says Rui A. Gonçalves.

Clinical signs

Evaluating mycotoxin contamination is not a common practice since clinical signs on their effects in specific species have not been well investigated. Unlike in livestock where there are specific clinical signs for each mycotoxin, in aquaculture species, clinical signs are generally inexistent or subclinical.

Mycotoxin contamination could represent a hidden problem which can lead to increased disease susceptibility and poor performance. There is the general effect of suppression of feed intake but then, it was pointed out, many adverse conditions affect feed intake. A common reported impact has been in liver and gut health which are associated with immunosuppression. Gonçalves noted, “Clinical signs are generally misleading or easily associated with other pathogens.”

Some clinical signs for specific mycotoxins were discussed. Fumonisins contamination is common in corn and the target organs are liver, kidney and the brain. A reduction in weight gain and lesions in the mouth occurred in carp fed with 500ppb fumonisins, according to Petrinec et al. (2004). A synergistic effect with aflatoxin B1 (AFB 1 ) has been well established.