The vulnerability of fish species to mycotoxins has been recognised since the 1960s. Since then diets for farmed fish species have changed significantly with plant proteins and energy sources from oilseed meals and cereal grains replacing traditional feed raw materials derived from animals. Today around 95% of fish feed ingredients come from plant sources. Consequently, commercially farmed aqua species are as much at risk from mycotoxins as land-based livestock.
Certain fish species are more susceptible to mycotoxicoses than others with rainbow trout generally being one of the most sensitive to the effects of mycotoxins. Shrimp are also often more sensitive to toxicity of mycotoxins than other species. On the other hand, catfish are typically considered to be a more resistant fish species to mycotoxins.
Key mycotoxins produced by Aspergillus moulds
Aflatoxin-contaminated cottonseed meal was identified as the causative agent of impaired performance and high mortality in farmed trout in the USA as early as 1960. However, aflatoxin metabolism does appear to differ between different fish species, which means some are more susceptible to poisoning than others.
Signs of aflatoxicosis in fish include:
- Poor growth and feed efficiency
- Cancerous tumours
- Pale gills
- Kidney abnormalities
- Liver damage
- Immune suppression
- High or spiking mortality
When exposed to ochratoxin contaminated feed, reduced growth, kidney and liver lesions, poor feed efficiency and high mortalities have all been reported in several aqua species.
Key mycotoxins produced by Fusarium moulds
The toxic effects of Fumonisins (derived from maize) have been mainly studied in channel catfish, which can tolerate up to 20ppm in commercial feed without any loss of performance. However, contamination around this level has also been more recently shown to cause immunological changes. Fumonisins have also been shown to cause damage to blood vessels, liver, pancreas, kidney, heart and brain tissue in carp.
Zearalenone acts as a hormone analogue (mimic) in terrestrial animals and appears to exert the same effect in fish. Testicular damage has been reported in carp when the fish were fed maize diets contaminated with a high levels if zearalenone.
Studies with rainbow trout and channel catfish have shown that T-2 toxin can cause major damage to the gut and mucosa accompanied by severe odema. Younger fish are more susceptible than older ones.
Cyclopiazonic acid is actually more toxic to channel catfish than aflatoxin. Prolonged exposure leads to poor growth and the formation of protein granules in kidney epithelium and necrosis of gastric glands.
DID YOU KNOW?
Like other vertebrates, fish are more sensitive to mycotoxins when multiple forms are present in the feed. A mycotoxin may be present at a ‘safe’ level in isolation, but when combined with another mycotoxin (also at a ‘safe’ level on its own) both can act synergistically to produce a toxic effect in the fish.
The symptoms can be many and varied, but the outcome in all cases will be reduced performance and lost profits.
Effective mycotoxin management is about seeing the whole challenge, from the farm to feed mill and from risk assessment to feed management. The Alltech Mycotoxin Management Team provide a number of solutions to help you mitigate the threat you could face from field or storage mycotoxins. To find out more click here.