Metabolic responses of channel catfish (Ictalurus punctatus) exposed to phenol and post-exposure recovery.

Metabolic adjustments were studied in channel catfish Ictalurus punctatus exposed to 1.5 mg L-1 of phe nol (10% LC50) for four days and recovered for seven days. Lower triacylglycerol (TGA) stores and increased muscle fat free acids (FFA) suggest fat catabolism in muscle. Remarkable liver FFA decrease (-31%) suggests liver fat catabolism as well. Increased muscular ammonia levels and ASAT (aspartate aminotransferase) and decreased plasma aminoacids suggest higher muscular amino acid uptake. Constant levels of glucose and increased liver glycogen stores, associated with lower amino acids in plasma, indicate gluconeogenesis from amino acids. This is supported by higher hepatic ALAT and ASAT. Higher hepatic LDH followed by lower plasma lactate may indicate that plasma lactate was also used as gluconeogenic substrate. Biochemical alterations were exacerbated during the post-exposure recovery period. Reduction in muscle and plasma protein content indicate proteolysis. A higher rate of liver fat catabolism was resulted from a remarkable decrease in hepatic TGA (-58%). Catabolic preference for lipids was observed in order to supply such elevated energy demand. This study is the first insight about the metabolic profile of I. punctatus to cope with phenol plus its ability to recover, bringing attention to the biological consequences of environmental contamination.

Δ6-fatty acid desaturase and fatty acid elongase mRNA expression, phagocytic activity and weight-to-length relationships in channel catfish (Ictalurus punctatus) fed alternative diets with soy oil and a probiotic.

A time-course feeding trial was conducted for 120 days on juvenile channel catfish (Ictalurus punctatus) to study the effects of diets differing in oil source (fish oil or soy oil) and supplementation with a commercial probiotic. Relative levels of Δ6-fatty acid desaturase (Δ6-FAD) and fatty acid elongase (FAE) expression were assessed in brain and liver tissues. Both genes showed similar expression levels in all groups studied. Fish weight-to-length relationships were evaluated using polynomial regression analyses, which identified a burst in weight and length in the channel catfish on day 105 of treatment; this increase was related to an increase in gene expression. Mid-intestinal lactic acid bacterium (LAB) count was determined according to morphological and biochemical criteria using API strips. There was no indication that intestinal LAB count was affected by the modified diets. The Cunningham glass adherence method was applied to evaluate phagocytic cell activity in peripheral blood. Reactive oxygen species (ROS) generation was assessed through the respiratory burst activity of spleen macrophages by the NBT reduction test. Probiotic-supplemented diets provided a good substrate for innate immune system function; the phagocytic index was significantly enhanced in fish fed soy oil and the probiotic, and at the end of the experimental period, ROS production increased in fish fed soy oil. The substitution of fish oil by soy oil is recommended for food formulation and will contribute to promoting sustainable aquaculture. Probiotics are also recommended for channel catfish farming as they may act as immunonutrients.

In vitro kinetics of hepatic albendazole sulfoxidation in channel catfish (Ictalurus punctatus), tilapia (Oreochromis sp.), rainbow trout (Oncorhynchus mykiss) and induction of EROD activity in ABZ-dosed channel catfish.

Liver microsomes from market-size (n = 6) rainbow trout, channel catfish and tilapia were used to investigate in vitro biotransformation kinetics of albendazole (ABZ). ABZ was transformed to a single metabolite, ABZ sulfoxide (ABZ-SO). Catfish displayed the highest maximal velocity (V(max) = 264.0 +/- 58.6 pmols ABZ-SO/min/mg protein) followed by tilapia (112.3 +/- 8.2) and rainbow trout (73.3 +/- 10.3). V(max) in catfish was significantly different (P < 0.05) from the other two species. Michaelis-Menten constant (K(m)) values (microm) varied significantly among the species: rainbow trout (3.9 +/- 0.5), tilapia (9.2 +/- 1.7) and catfish (22.0 +/- 3.2). However, V(max)/K(m) ratios showed no difference among the three species, making them equally efficient performing this phase I biotransformation reaction. In a second series of experiments, channel catfish (n = 6 per treatment) were dosed in vivo with gel-food containing ABZ (10 mg/kg, p.o.). Fish were killed at 24, 48, 72 and 120 h after dosage. Control fish were fed ABZ-free feed. Induction of ethoxyresorufin-o-deethylase activity was significant (P < 0.05) in all ABZ-dosed treatments as compared with controls.

Biochemical studies of taste sensation--VIII. Partial characterization of alanine-binding taste receptor sites of catfish Ictalurus punctatus using mercurials, sulfhydryl reagents, trypsin and phospholipase C.

1. Taste receptors for L-alanine in the channel catfish Ictalurus punctatus have been partially characterized. The binding activity, which is localized to a sedimentable fraction (Fraction P2), was assayed with L-[3H]alanine as the ligand. 2. Addition of HgCl2 or p-mercuribenzoate to the assay at 0.1-1 mM markedly inhibited binding. The effect was not reversible and was unaffected by increased L-alanine in the binding assay. 3. The sulfhydryl reagents iodoacetate, 5,5'-dithiobis(2-nitrobenzoic acid), arsenite, and N-ethylmaleimide did not show appreciable inhibition of binding. The results suggest that the inhibitory effect of mercurials is not on specific sulfhydryl groups at alanine-binding sites. 4. Treatment of Fraction P2 with phospholipase C decreased binding activity and treatment with trypsin led to increased binding activity.