John M. Grizzle

An Iridovirus Isolated from Wild Largemouth Bass

Abstract During July through September 1995, about 1,000 adult largemouth bass Micropterus salmoides died in Santee-Cooper Reservoir, South Carolina. Necropsy of two moribund largemouth bass (each weighing about 2 kg and measuring about 50 cm) revealed no parasites or bacterial infection. Fathead minnow (FHM) cell cultures inoculated with filtered homogenate from the swim bladder of one fish and the swim bladder and liver of the second fish developed cytopathic effect 48 h after inoculation. Media from infected cell cultures contained up to 108.9 TCID50/mL of a 0.45-μm filterable agent (TCID50 is the tissue culture infective dose that affects 50% of innoculated cultures). Electron microscopy of infected FHM cells revealed a cytoplasmic, icosahedral virion that averaged 132 nm from facet to facet and 145 nm from corner to corner. Viruses acquired an envelope upon passing through the plasma membrane. Studies of virus replication inhibition by pyrimidine analogs were inconclusive in classifying the nucleic a...

Towards the Ictalurid Catfish Transcriptome: Generation and Analysis of 31,215 Catfish ESTs.

BackgroundEST sequencing is one of the most efficient means for gene discovery and molecular marker development, and can be additionally utilized in both comparative genome analysis and evaluation of gene duplications. While much progress has been made in catfish genomics, large-scale EST resources have been lacking. The objectives of this project were to construct primary cDNA libraries, to conduct initial EST sequencing to generate catfish EST resources, and to obtain baseline information about highly expressed genes in various catfish organs to provide a guide for the production of normalized and subtracted cDNA libraries for large-scale transcriptome analysis in catfish.ResultsA total of 17 cDNA libraries were constructed including 12 from channel catfish (Ictalurus punctatus) and 5 from blue catfish (I. furcatus). A total of 31,215 ESTs, with average length of 778 bp, were generated including 20,451 from the channel catfish and 10,764 from blue catfish. Cluster analysis indicated that 73% of channel catfish and 67% of blue catfish ESTs were unique within the project. Over 53% and 50% of the channel catfish and blue catfish ESTs, respectively, had significant similarities to known genes. All ESTs have been deposited in GenBank. Evaluation of the catfish EST resources demonstrated their potential for molecular marker development, comparative genome analysis, and evaluation of ancient and recent gene duplications. Subtraction of abundantly expressed genes in a variety of catfish tissues, identified here, will allow the production of low-redundancy libraries for in-depth sequencing.ConclusionThe sequencing of 31,215 ESTs from channel catfish and blue catfish has significantly increased the EST resources in catfish. The EST resources should provide the potential for microarray development, polymorphic marker identification, mapping, and comparative genome analysis.

Growth and hepatic lesions of Nile tilapia (Oreochromis niloticus) fed diets containing aflatoxin B1

Abstract Responses of Nile tilapia to varying concentrations of aflatoxin B 1 (AFB) were investigated under controlled laboratory conditions. Nile tilapia (2.7 g) were fed semipurified diets containing 0, 0.25, 2.5, 10, or 100 mg AFB/kg of diet for 8 weeks. Weight gain and hematocrit of fish fed with 0.25 mg AFB/kg were not significantly different from that of the control; however, diets containing higher levels of AFB had significantly ( P

Growth and body composition of channel catfish (Ictalurus punctatus) fed diets containing various percentages of canola meal

A 12-week feeding trial was conducted in aquaria with juvenile (10 g) channel catfish to examine the effects of partially substituting canola meal for soybean meal in prepared diets. Six isonitrogenous (32% protein) and isocaloric (2.7 kcal digestible energy g−1) diets were formulated to contain 0, 12, 24, 36, and 48% canola meal (CM). There were two diets with 0% CM; one with 8% fish meal (FM) and one with 4% FM. All diets with CM had 4% FM. Fish were fed twice daily all they could consume in 20 min. After 12 weeks, fish fed a diet with 8% FM and 0% CM had significantly higher (P < 0.05) percentage weight gains than fish fed all other diets. Fish fed diets containing 12 and 36% CM had significantly higher (P < 0.05) percentage weight gains (average 604%) than fish fed a diet containing 48% CM. Feed conversion ratio (FCR) of fish fed a diet containing 48% CM was significantly (P ≤ 0.05) higher (2.25) than values for fish fed 12, 24, and 36% CM. There were no histological differences in the thyroid of fish fed any of the diets. These data suggest that channel catfish can be fed diets containing up to 36% CM without adverse effects on growth or body composition. Fish fed a diet with 48% CM had a lower percentage weight gain compared with fish fed diets containing between 12 and 36% CM, possibly due to reduced palatability of the diet. Use of canola meal in practical diets for channel catfish may allow producers and feed mills to formulate more economical diets by adding another plant protein source to ingredients used in commercial catfish diets.

Effects of nonylphenol on the gonadal differentiation of the hermaphroditic fish, Rivulus marmoratus

Nonylphenol (NP) is an estrogenic degradation product of alkylphenol polyethoxylate surfactants. In this study, the effects of NP on gonadal differentiation and development in Rivulus marmoratus (Osteichthyes, Cyprinodontiformes), a self-fertilizing, hermaphroditic species, were examined. Starting at hatching, fish were exposed to 150 or 300 microg 1(-1) NP (nominal concentrations) in a static system with daily renewal. The measured concentration of NP in the test water decreased rapidly; half-life was 8.0 h. After 60 d of exposure to NP, fish were kept in uncontaminated water for 20 d and were then preserved for histological examination. No fish exposed to 300 microg l(-1) NP (N=8) and only two of nine fish exposed to 150 microg l(-1) NP developed testicular tissue, compared with nine of 13 water-control fish and five of nine solvent-control fish. Oogenesis was also significantly inhibited by NP. None of the fish exposed to 300 microg l(-1) and only two of nine fish exposed to 150 microg l(-1) NP had vitellogenic oocytes, compared with seven of 11 water-control fish (not including males) and six of nine solvent-control fish. Dysplasia of the gonadal lumen also occurred in fish exposed to 300 microg l(-1) NP. These changes, including testicular agenesis, have not been previously reported in fish exposed to NP.

Monoclonal antibody-based immunoassay of vitellogenin in the blood of male channel catfish (Ictalurus punctatus).

1. A monoclonal antibody to vitellogenin of channel catfish (Ictalurus punctatus) was made, and its specificity was demonstrated using Western blots of serum from female fish, estradiol-treated male fish, untreated male fish, vitellogenin purified by three different methods and egg extracts. 2. An enzyme-linked immunosorbent assay (ELISA), using this monoclonal antibody, detected vitellogenin in the plasma of 59 out of 60 untreated 17-24-month-old male channel catfish with a mean concentration of 338 micrograms/ml and a maximum concentration of 4240 micrograms/ml. 3. Vitellogenin levels in male channel catfish were unrelated to testicular stage, gonadosomatic index and month.

Survival of Caught and Released Largemouth Bass after Containment in Live Wells

Abstract Survival of angled largemouth bass Micropterus salmoides held in live wells for 3–9 h, with and without a water conditioner, was compared to largemouth bass released within 30 min (immediate release) of capture. The study was set up to simulate conditions that may occur during a largemouth bass tournament. Simulated tournaments were held in August, November, February, May, and July. Survival of prerelease and postrelease fish was higher when water temperatures were cool during fall and winter. Survival of largemouth bass released within 30 min was 98.9%, which was higher (P < 0.01) than survival of fish held in live wells without a water conditioner (90.8%). Fish held for 3–9 h in live wells with a water conditioner had a 96.5% survival, which was higher (P < 0.05) than survival for those held in unconditioned water. Largemouth bass caught in July had higher mortality than fish caught in November, February, or May. Indications are that addition of a water conditioner to live wells enhances surviv...

First Report of Yersinia ruckeri Biotype 2 in the USA

A polyphasic characterization of atypical isolates of Yersinia ruckeri (causative agent of enteric redmouth disease in trout) obtained from hatchery-reared brown trout Salmo trutta in South Carolina was performed. The Y. ruckeri isolates were biochemically and genetically distinct from reference cultures, including the type strain, but were unequivocally ascribed to the species Y. ruckeri, based on API 20E, VITEK, fatty acid methyl ester profiles, and 16S rRNA gene sequencing analysis. These isolates were nonmotile and unable to hydrolyze Tween 20/80 and were therefore classified as Y. ruckeri biotype 2. Genetic fingerprint typing of the isolates via enterobacterial repetitive intergenic consensus (amplified by polymerase chain reaction) and fragment length polymorphism showed biotype 2 as a homogeneous group distinguishable from other Y. ruckeri isolates. This is the first report of Y. ruckeri biotype 2 in the USA.

Nitrite-Induced Predisposition of Channel Catfish to Bacterial Diseases

Abstract Channel catfish, Ictalurus punctatus, continuously exposed to 6 mg/L (ppm) nitrite and intraperitoneally injected with Aeromonas hydrophila had lower bacterial median lethal doses (LD50) than control fish. The clearance rate of injected A. hydrophila was reduced in fish chronically exposed to 5 mg/L (ppm) nitrite. Flexibacter columnaris infections occurred spontaneously in channel catfish exposed to 5 mg/L (ppm) nitrite for 7 days. None of the control fish became infected with F. columnaris.

Acute Toxicity of Aflatoxin B1 to Channel Catfish

Abstract Both oral and intraperitoneal (IP) administration of 12 mg aflatoxin B1 (AFB1) per kilogram of body weight caused regurgitation of stomach contents by channel catfish Ictalurus punctatus. Detoxification of AFB1 (ammoniation) significantly reduced the incidence of regurgitation. The 10-d median lethal dose (LD50; dose that is lethal to 50% of test organisms) for IPadministered AFB, in channel catfish averaging 19 g was 11.5 mg/kg of body weight, with a 95% confidence interval of 9.5–13.3 mg/kg. Gills, livers, kidneys, spleens, stomachs, and intestines of moribund fish injected with 12 mg AFB1/kg of body weight were extremely pale. Hematocrits, hemoglobin concentrations, and erythrocyte counts of moribund fish were about 10% of those values in control fish. Histological lesions in moribund fish included sloughing of intestinal mucosa and necrosis of hematopoietic tissues, hepatocytes, pancreatic acinar cells, and gastric glands. Spleens showed reduction in volume of the red pulp and reduction in nu...