R. O. Sinnhuber

NEOPLASMS IN RAINBOW TROUT, A SENSITIVE ANIMAL MODEL FOR ENVIRONMENTAL CARCINOGENESIS*

The following topics are discussed: susceptibility of rainbow trout (Salmo gairdneri) to aflatoxins and other mycotoxins; the Oregon test diet; carcinogenic effects of cyclopropenoid fatty acids; carcinogenic response of the rainbow trout embryo; metabolism of mycotoxins by rainbow trout; and pathogenesis of rainbow trout liver cancer. (HLW)

Effect of dietary ω3 and ω6 fatty acids on growth and feed conversion efficiency of coho salmon (Oncorhynchus kisutch)

Abstract Sixteen isocaloric diets varying only in the levels of ω3 and ω6 fatty acids were prepared. Each diet was fed to duplicate groups of coho salmon for 14 weeks. At termination, the final weight of each diet group fish was determined. The optimum level of dietary ω3 fatty acid ranged from 1% to 2.5%. Dietary ω6 fatty acid higher than 1% depressed fish growth. Fish growth, feed conversion efficiency, fish mortality and fatty acid composition of fish phospholipids were determined.

Effect of dietary linolenic acid and docosahexaenoic acid on growth and fatty acid composition of rainbow trout (Salmo gairdneri).

Methyl linolenate 18∶3ω3 and docosahexaenoate 22∶6ω3 were incorporated in semipurified diets at several levels and fed to trout previously maintained on a fat-free diet. After 14 weeks, the weight gain and feed conversion of the fish on each diet were determined. The fatty acid composition of the lipid from each group of fish was analyzed by gas liquid chromatography. Both 18∶3ω3 and 22∶6ω3 fed at the 1% level supported maximum growth of the fish. The control group, which were fed no ω3 fatty acids, exhibited a shock syndrome, poor appetite and a very slow growth rate. Tissue fatty acid analysis revealed eicosatrienoic acid 20∶3ω9 accumulated in the phospholipid fraction of this group. The 20∶3ω9 level was lowered when either 18∶3ω3 or 22∶6ω3 was included in the diet. Analysis showed that the dietary 18∶3ω3 was rapidly converted by the fish into 22∶6ω3 with a high concentration in the phospholipid. However 22∶6ω3 fed to the fish remained unchanged and little or no retroconversion of this fatty acid was observed.

Effect of dietary lipids on fatty acid composition of body lipid in rainbow trout (Salmo gairdneri)

Three isocaloric diets were prepared. Diet 1 (Control) contained 22% herring oil. In diets 2 and 3, a third and a half of the herring oil was replaced, respectively, by an animal fat (lard) which contained a high percentage of saturated fatty acids. Each diet was fed to duplicate groups of rainbow trout for 14 wk. The results of the feeding trial indicated that the concentration of the saturated fatty acids in trout body lipid did not increase despite the high concentration of these fatty acids in Diets 2 and 3. Fish growth, feed efficiency, mortality and the level of fatty acid deposited in fish body lipid and phospholipids are discussed.

Effect of dietary linolenic and linoleic acids upon growth and lipid metabolism of rainbow trout (Salmo gairdneri)

Nine diets, each containing different levels of linoleic acid (18∶2ω6) and linolenic (18∶3ω3) were fed to duplicate groups of rainbow trout for 14 weeks. The growth rate, feed efficiency, accumulated mortality, and fatty acid composition of neutral fat and phospholipids of these groups of fish were determined. The growth was slow in the groups of fish receiving diets containing (A) low concentration of 18∶3ω3 and (B) high concentration (5%) of 18∶2ω6. The accumulated mortality was high in these groups of fish. The diet containing 1% 18∶3ω3 alone supported rapid fish growth with low mortality. The feed efficiency of this diet was also high. The metabolism of 18∶2ω6 and 18∶3ω3 in fish and their conversion to more unsaturated fatty acids typical of fish lipids was investigated.

Acute intraperitoneal toxicity of ochratoxins A and B in rainbow trout (Salmo gairdneri)

Abstract The acute intraperitoneal toxicities of two metabolites of Aspergillus ochraceus , ochratoxins A and B, and their dihydroisocoumarin derivatives, ochratoxins a and b , were studied in 6-month-old Mt. Shasta strain rainbow trout ( Salmo gairdneri ). Ochratoxin A was the only compound found to be lethal to trout at the levels administered, its acute intraperitoneal LD 50 being 4·67 mg/kg. Pathological changes in the liver and kidneys were produced by ochratoxins A and B but not by ochratoxin a or b . Ochratoxin A produced degenerative changes in the hepatic parenchymal cells, including nuclear swelling and cytoplasmic and nuclear lipid vacuolation, necrosis in the proximal tubules, haematopoietic tissue and glomeruli of the kidneys and pycnotic nuclei, cast formation and lipid vacuolation in the renal tubules. Ochratoxin B administered at levels up to 66·7 mg/kg caused no deaths but the highest dose induced pathological changes in the liver and kidneys similar to those produced by relatively low levels of ochratoxin A. Ochratoxins a and b administered at levels up to 28·0 and 26·7 mg/kg, respectively, failed to cause any deaths or induce any microscopic lesions that were not seen in control trout dosed with 0·1 n -sodium bicarbonate. It is suggested that ochratoxins A and B are metabolized to their non-toxic water-soluble dihydroisocoumarin moieties, which are readily excreted.

Effect of steroid hormones on the growth of juvenile coho salmon (Oncorhynchus kisutch)

Abstract Two androgens, 17 α-methyltestosterone and testosterone, and an estrogen, estradiol, were individually incorporated in test diets at 2.5 mg/kg dry diet and fed to coho salmon for 14 weeks. The fish weight gain, feed conversion efficiency, fish body composition and fatty acid composition of fish body lipids were determined. The three steroid hormones all accelerate the growth rate of fish. The 17 α-methyltestosterone supplementation promotes significantly greater fish weight gain and feed efficiency. Results of histologic examination of fish liver, kidney, heart, and gonad are discussed.

The effect of dietary sterculic acid on the hepatic lipids of rainbow trout.

Groups of young rainbow trout (5 g) were fed a basal diet containing 9% salmon oil and 1% tristearin with 0, 100 or 200 ppm methyl sterculate. Liver lipids were separated into polar and nonpolar fractions and the fatty acids quantitatively analyzed. Significant elevations of the stearic-oleic and the palmiticpalmitoleic ratios were found in liver fatty acid composition 10 days after the feeding trial began. Liver triglycerides of fish fed methyl sterculate for 87 days contained only 2–3% docosahexenoic acid as compared to 10.69% in control trout, suggesting an effect on the biosynthesis of long chain polyunsaturates. Dietary cyclopropenoid fatty acids (CPFA) suppressed growth rate during the first part of the 200 day feeding trial. After 90 days no differences in the rate of weight gain were observed between the control and CPFA groups. A seven day feeding trial with 0, 5, 20, 50 and 100 ppm CPFA resulted in a maximum change in the stearic-oleic ratio at 50 and 100 ppm levels. All levels of CPFA increased this ratio and caused marked alterations in the cellular morphology of the liver.

Comparative rates of hydrolysis of ochratoxins A and B in vitro.

The rates of hydrolysis of ochratoxins A and B in vitro by the enzyme, bovine carboxypeptidase A, and by enzymes in tissue extracts of rat liver, small intestine and large intestine were studied. The Vmax values for the hydrolysis of ochratoxins A and B by carboxypeptidase are 5·15 × 10−7 and 4·35 × 10−5 moles/litre/min, respectively. Incubation of the extracts of rat tissue with an equimolar amount of ochratoxin A or B indicated that ochratoxin B was hydrolysed 6–7 times faster than ochratoxin A. It is suggested that this difference in hydrolysis rate may partly account for the difference in toxicity of ochratoxins A and B.

An improved 2-thiobarbituric acid (TBA) procedure for the measurement of autoxidation in fish oils

An improved 2-thiobarbituric acid (TBA) method suitable for routine testing of autoxidative changes of fish oil and other polyunsaturated lipids has been developed. Air oxidation of the lipid during the TBA reaction was found to produce misleading results. The air oxidation may be controlled by addition of antioxidants to the reaction system. Other factors causing inconsistent TBA results and methods of prevention are also described. A comparison of peroxide and TBA values in autoxidized menhaden oil is presented.