Can Fumonisins negatively affect aquaculture species
What are fumonisins?
Fumonisins (FUM) are a group of mycotoxins produced by a number of Fusarium species, notably F. verticillioides, F. proliferatum, and F. nygamai, and the most common mycotoxin is fumonisin B1 (FB1). Fumonisins are characterized by their long-chain hydrocarbon unit (similar to that of sphingosine and sphinganine) which plays a role in their toxicity (Wang, Ross et al. 1992). Fumonisins inhibit a key enzyme in lipid metabolism (sphinganine / sphingosine N-acyltransferase (ceramide synthase)), disrupting this pathway and leading to toxicity.
Global increase in fumonisins
The occurrence of fumonisins, levels of contamination, and implications of mycotoxins entering the feed production chain by the inclusion of cereal grains have gained importance globally over the last few years, and aquaculture is no exception. Figure 1 shows the prevalence of fumonisins in corn, one of the major commodities affected by this group of toxins. There is a trend towards higher fumonisin levels in corn worldwide since 2015 and this trend is also reflected in other commodities commonly used in aquafeed production.
Fumonisins impact growth rate and feed efficiency
In aquaculture, fumonisins have generally been associated with reduced growth rate, feed consumption, feed efficiency, and impaired sphingolipid metabolism (Goel, Lenz et al. 1994; Li, Raverty et al. 1994; Lumlertdacha and Lovell 1995; Tuan, Manning et al. 2003). However, there is little information on the eﬀects of fumonisins on carnivorous aquaculture species, with most of the available research focusing on freshwater species.
The channel catfish (Ictalurus punctatus) is the most widely-studied species (Goel, Lenz et al. 1994; Li, Raverty et al. 1994; Lumbertdacha, Lovell et al. 1995; Lumlertdacha and Lovell 1995) and, according to the authors cited, these fish can tolerate relatively high levels of FUM, with a sensitivity level of around 10 mg FB/kg feed. Adverse effects of fumonisin-contaminated diets have also been reported in carp (Cyprinus carpio L.): one-year-old carp showed signs of toxicity at 10,000 µg FB1/kg feed (Petrinec, Pepeljnjak et al. 2004). This experiment discovered scattered lesions in the exocrine and endocrine pancreas and interrenal tissue, probably due to ischemia and/or increased endothelial permeability. In another study, one-year-old carp were fed pellets contaminated with 500, 5,000 or 150,000 µg FB1/kg body weight, causing body weight loss and disruption to hematological and biochemical parameters in the target organs (Pepeljnjak, Petrinec et al. 2003).
Tuan et al. (2003) demonstrated that feeding FB1 to fingerlings of the tropical species, Nile tilapia (Oreochromis niloticus), at levels of 10, 40, 70 and 150 mg kg/feed for 8 weeks reduced growth. In particular, fish fed diets containing FB1 at levels of 40,000 µg/kg or higher had decreased average weight gains. Hematocrit only decreased in the tilapia fed a diet containing 150,000 µg FB1 kg/ feed. The ratio of free sphinganine to free sphingosine (Sa:So ratio) in the liver increased at 150,000 µg FB1 kg/ feed.
FB1 has not been extensively studied as a shrimp feed contaminant, however the few studies available suggest that Pacific whiteleg shrimp (Litopenaeus vannamei) is much more sensitive to FB1 than some other freshwater species. García-Morales et al. (2013) demonstrated a reduction in soluble muscle protein concentration and changes in myosin thermodynamic properties in whiteleg shrimp fed 20 to 200 µg/kg FB1 after 30 days of exposure. The same authors reported marked histological changes in the tissues of shrimp fed FB1 at 200 µg/kg feed, and meat quality changes after 12 days of ice storage when shrimp were fed more than 600 µg/kg feed.
Marine species are more susceptible
As mentioned before, all the aquaculture species tested for sensitivity to FUM have been omnivorous or herbivorous, and all have been freshwater species, except whiteleg shrimp.
High levels of FUM have been found in plant meals commonly used for carnivorous species, so BIOMIN conducted a trial, to be published soon, with gilthead seabream (Sparus aurata), one of the most important aquaculture species farmed in Europe and a good model to study the effect of FUM on carnivorous marine species. In this trial, triplicate groups of 35 seabream, with a mean initial body weight (IBW) of 28.8 ± 2.1 g were fed one of 3 experimental diets for 60 days. The experimental diets were: Control diet, free of mycotoxins; FUM 1 feed, containing 168 µg FUM/kg; and FUM 2 feed, containing 333 µg/FUM kg.
Preliminary results demonstrated that the contamination levels tested affected overall growth. Table 1 summarizes the effect of FUM 1 and FUM 2 on the main growth indicators: final body weight (FBW), specific growth rate (SGR), feed conversion ratio (FCR), feed intake (FI) and protein efficiency ratio (PER). The FUM levels tested did not affect survival.
Table 1. Effect of FUM on main growth indicators (compared to the Control group).
|FUM 1||↓ 11.4%||↓ 8.2%||↑ 17.5%||↑ 10.9%||↓ 14.9%|
|FUM 2||↓ 15.7%||↓ 11.9%||↑ 19.3%||↑ 9.5%||↓ 16.1%|
These data are interesting in view of the following facts: firstly, because (as far as we are aware) this is the first trial conducted with a marine species. Secondly, the levels of FUM added to the feed were within the levels of contamination frequently found in commercial aquafeeds.
Marine species may be highly sensitive to fumonisins, and relatively low levels of FUM (< 1,000 µg kg/ feed) can already impact growth and immune status. This is an additional concern for the marine aquaculture sector, as the European Commission (EC) guidance values for fumonisins B1 + B2 in complementary and complete feedingstuffs for fish is 10 mg FUM kg/ feed (European Commission 2006), which may be too high, at least for Sparus aurata and Litopenaeus vannamei. Further research is required to confirm whether other marine species are as sensitive to FUM as seabream.