Dehai Xu

Effect of cooking on residues of ormetoprim and sulfadimethoxine in the muscle of channel catfish

Channel catfish Ictalurus punctatus were fed Romet medicated feed at doses of 25, 50, and 100 mg Romet per kg of fish daily for 5 d. To keep Romet concentration high enough for evaluation of cooking effects, fillets were sampled without the 3 d withdrawal period required by the US Food and Drug Administration. Concentrations of ormetoprim (OMP) and sulfadimethoxine (SDM), the antibiotics in Romet, were determined by a high-pressure liquid chromatography method in fillets before and after cooking. Fillets were cooked by one of four methods: smoked at 160–200 °C, baked at 190 °C, fried in canola oil at 190 °C, and injected with a mixture of 6% polyphosphate solution, frozen for 4 weeks, and then fried in vegetable oil at 190 °C. The average OMP concentrations in cooked tissue were 0.23, 0.66, and 1.22 μ/g dry basis (db) and SDM concentrations were 2.64, 2.73, and 3.74 μg/g db for fish dosed with Romet at levels of 25, 50, and 100 mg/kg, respectively. Cooking caused an average 54.0% reduction of OMP and 46.1% reduction of SDM from raw fillet of fish. Cooking significantly reduces both OMP and SDM residues in fillets and provides an additional margin of safety for consumers. Results for the four cooking methods were not statistically different.

Formaldehyde Residue in Striped Bass Muscle

Abstract Tissue residues of formaldehyde were determined for striped bass Morone saxatilis of three size-groups (total length, mean ± SD): 13.0 ± 0.9 cm, 15.5 ± 2.8 cm, and 33.9 ± 1.9 cm. The experiments conducted were a 144-h exposure to a static solution of 25 mg formalin/L (9.3 mg formaldehyde/L) and a 1-h exposure to a static solution of 250 mg formalin/L (92.5 mg formaldehyde/L). There were no statistical differences between formaldehyde residues in untreated (control) fish and fish exposed to 25 mg formalin/L for 24 h, but exposed fish did have significantly higher formaldehyde residues after 48 and 72 h of this treatment. Formaldehyde levels were back to normal after 96 h. Muscle formaldehyde residues were not significantly different between treated and control fish after treatment with 250 mg formalin/L. Additional formaldehyde was produced in tissues of control fish during decomposition during storage.

Electron Microscopy of Infection by Saprolegnia spp. in Channel Catfish

Abstract Saprolegnia sp. isolated from channel catfish Ictalurus punctatus grew slower than S. parasitica on cornmeal agar (CMA). Oogonia in Saprolegnia sp. appeared frequently, whereas oogonia were rarely seen in S. parasitica on CMA. In experimental exposures of injured channel catfish to fungal spores, infections were apparent after 3–4 d, but were most common after 7–9 d. Multiple lesions were usually seen in naturally infected fish, whereas a single lesion appeared at the injured site of experimentally infected fish. No obvious differences were found between lesions caused by S. parasitica and those caused by Saprolegnia sp. Most of the epidermal cells in fungusinfected lesions were necrotic. In some lesions, the epidermis was completely sloughed and the dermis was exposed. Both Saprolegnia parasitica and Saprolegnia sp. penetrated the dermis, causing damage to fibroblasts and collagen lamellae.

Oxytetracycline Residue in Striped Bass Muscle

Abstract Tissue residues were measured in striped bass Morone saxatilis that had been injected intraperitoneally with 50 mg oxytetracycline (OTC)/kg or had been fed a ration containing 75 mg OTC/kg of fish daily for 10 d. Concentration of OTC in muscle of fish fed medicated feed was below the quantitation limit in 67% of the fish 12 d after treatment and was below the quantitation limit in all fish after 16 d at 23°C. The calculated terminal elimination rate constant (β) was 0.20/d (range, 0.15–0.37/d), and the half-life was 2.7 d (range, 1.9–4.5 d). The concentration of OTC in muscle after intraperitoneal injection was below the quantitation limit after 24 d at 23°C. The β-value was 0.34/d and half-life was 2.0 d in fish injected with OTC intraperitoneally.

Communications: Protective Immunity Induced by a Commercial Vibrio Vaccine in Hybrid Striped Bass

Abstract Commercial Vibrio anguiliarum-V. ordalii bacterin was used to vaccinate hybrid striped bass (Morone saxatilis ♀ × M. chrysops ♂) to test the vaccine efficacy against vibriosis. Vaccination by direct immersion of fish in diluted Vibrio vaccine for 20 s resulted in increased protective immunity. The relative percent survival of hybrid striped bass challenged 35 d after vaccination was 66.7% for those challenged by 1-h immersion exposure to 7.03 × 107 V. anguillarum cells/mL, 75.0% for those challenged by injection with 3.51 × 105 cells/fish, and 86.7% for those challenged by injection with 3.51 × 104 cells/fish.

Changes in dieldrin and p,p'-DDE residues following cooking of channel catfish

The influence of cooking (frying, baking, and smoking) on dieldrin and 1,1-dichloro-2,2-bis[4-chlorophenyl]ethylene (DDE) residues in treated channel catfish ( Ictalarus punctatus ) was determined. Dieldrin and DDE were significantly reduced (P < 0.05) during cooking of catfish by 50 to 65% (dry basis) and 50 to 80%, respectively. Smoking resulted in maximum reduction (82%) of DDE residues, while baking resulted in the least reductions for both dieldrin (50%) and DDE (50%) when compared to the other preparation methods.

Ultrastructure of the hyphae of Saprolegnia parasitica.

Abstract Vegetative hyphae of Saprolegnia parasitica, a common parasitic fungus offish and fish eggs, are aseptate and have thin walls (30–90 nm). The hyphae contain large vacuoles and have elongate mitochondria and nuclei oriented parallel to the longitudinal axis and in the direction of hyphal extension. Presporangium hyphae, those hyphae that will form sporangia, also are aseptate, but have thicker walls (120–170 nm) and contain smaller vacuoles. Presporangium hyphae do not, in general, have the longitudinal orientation of organelles seen in vegetative hyphae. Densebody vesicles and primary bars, or encystment vesicles, as well as mitochondria, dictyosomes, and endoplasmic reticulum, are consistent features of these presporangium hyphae.