Page 778 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Aquatic Toxicology Chapter | 54 737

VetBooks.ir The threshold level of dietary meHg on spawning para- Ochratoxins
meters in fathead minnows is ,0.88 ppm.
OTA is nephrotoxic and immunotoxic in mammalian and

version in catfish when fed at 3 ppm OTA/kg of feed for
MYCOTOXINS avian species. OTA decreases weight gains and feed con-
8 weeks. A dose response was observed in histopathology
Important genera of fungi that produce mycotoxins are in the posterior kidney and liver. The lesions were
Fusarium, Aspergillus, and Penicillium (Coppock and enlarged melanomacrophage centers replacing kidney and
Jacobsen, 2009). These fungi, depending on growing con- pancreatic cells. The no effect dose for OTA in diet is
ditions, can be field and/or storage fungi and produce likely less than 1.0 mg OTA/kg of diet (See Chapter 72:
mycotoxins. Important growing conditions for mycotoxi- Ochratoxins and Citrinin).
genic fungi are temperature and moisture. A common
source of mycotoxins in fish feed is the use of grain
screenings as a feed ingredient. Important mycotoxins Trichothecenes
identified in aquaculture are fumonisins (FBs), monilifor-
The trichothecene group of mycotoxins is radiomimetic
min (MON), ochratoxin A (OTA), trichothecenes, zearale-
in toxicity and target rapidly dividing cells and cells
none (ZEA), and aflatoxins (AFs) (Greco et al., 2015). If
with high metabolic activity (Coppock and Jacobsen,
one mycotoxin is identified in a feed, it is most likely that
2009). The trichothecenes are also potent inhibitors of
other mycotoxins are present. There are species differ-
protein synthesis. All the trichothecenes studied are
ences between fish genera and species, and age in suscep-
immunotoxic. A common observation is reduced feed
tibility to mycotoxins. To some mycotoxins, e.g., AFs,
intake and feed refusal. The most common trichothecene
rainbow trout are uniquely sensitive.
identified in fish feeds is deoxynivalenol (DON).
Rainbow trout are sensitive to DON when fed at 2.0 ppm
DON/kg of feed for 8 weeks. DON is immunosuppres-
Fumonisins and Moniliformin
sive in fish and decreases native resistance to disease
Fish consuming contaminated feeds are exposed to FBs and growth. Toxicopathy of DON is subcapsular edema
of the liver, fatty infiltration of hepatocytes and hyaline
and MON (Coppock and Nation, 2012). Of the FBs, FB 1
is the most toxic. Fumonisins are structurally like sphin- droplet degeneration of tubular epithelial cells of the
gosine, and inhibit ceramide synthase, an enzyme in the caudal kidney. Feeding a diet containing 2 mg DON/kg
sphingolipid synthesis pathway. The effects of FB 1 on of feed for 23 days induced oxidative stress in rainbow
sphinganine sphingosine metabolism is an elevated trout. T-2 toxin is a potent trichothecene mycotoxin and
hepatic sphinganine/ sphingosine ratio and this can occur younger fish are at a greater risk for intoxication.
at dietary levels of 150 mg of FB 1 /kg of feed. Fish fed Feeding diets containing 1.5 5.0 T-2 toxin/kg of feed
diets containing 20, 80, 320, or 720 mg of FB 1 /kg of decreases growth, feed conversion, and diets with
feed for 2 years had dose response histopathologic .6.1 mg of T-2 toxin/fish (20-month-old) causes
changes in the liver. In all fish on the FB 1 diets the sloughing of the intestinal mucosa as casts without mor-
lesions were swollen hepatocytes with centrally located tality. The hemopoietic system is a target for T-2 toxin
nuclei and foci of hepatocytes containing clear cyto- and effects can be observed at dietary levels of 1.2 mg
plasm (likely contained lipids), hepatocellular necrosis T-2 toxin/kg of feed. T-2 toxin, in carp, causes anemia
and shrunken hepatocytes, (80 mg group). The hepato- and leukopenia, primarily a lymphopenia, at dietary
cytes with clear cytoplasm were near the central vein in levels of 5.3 mg T-2 toxin/kg of feed fed for 4 weeks.
the 20 mg/kg group and focally dispersed in the other Diet containing 0.625 mg of T-2 toxin/kg of feed fed for
treatment groups. 8 weeks cause reduction in growth. T-2 toxin-linked his-
Moniliformin inhibits pyruvate dehydrogenase in the topathology is stomach lesions consisting of multifocal
mitochondrial respiratory chain enzymes. Nile tilapia (O. lymphocytic infiltrates in the lamina propria and disrup-
niloticus), using weight gains and histopathology para- tion of normal submucosal glandular architecture with
meters, generally are more resistant to FB 1 than catfish. glandular loss. In the head kidney, hemopoietic areas
Diets containing 20 mg FB 1 or MON/kg of feed fed for 2 have decreased erythrocytic and myelocytic precursors.
weeks can depress growth in tilapia and catfish. MON has Macrophage aggregates are increased in head kidney.
been reported to cause cardiac myopathy in other species
studied (mammals and birds), but this does not appear to Zearalenone
have been reported for fish species. Catfish fed 120 mg
MON/kg of feed for 10 weeks had small nucula in liver Zearalenone, a resorcylic acid lactone, is associated with
cells. FB 1 is immunosuppressive in fish. DON contamination of cereal grains (Coppock and