Gary J. Carmichael

Cryopreservation of Channel Catfish Sperm: Storage in Cryoprotectants, Fertilization Trials, and Growth of Channel Catfish Produced with Cryopreserved Sperm

Abstract We developed methods for cryopreserving sperm of channel catfish Ictalurus punctatus and evaluated the use of cryopreserved sperm for reproduction. Five cryoprotectants were evaluated: Methanol, glycerol, dimethyl sulfoxide (DMSO), sucrose, and polyvinylpyrrolidone. We measured the motility of sperm that had been stored at 4°C in three concentrations of cryoprotectants (5%, 10%, 15%) dissolved in a modified Hanks balanced salt solution. All cryoprotectants reduced motility within 6 h; 5% methanol and 5% DMSO caused the smallest reduction. After sperm were frozen at –80°C and stored for 2 d at –196°C, motility was highest (5–10%) in samples cryopreserved with 5% and 10% solutions of methanol. Sperm cells cryopreserved in methanol solutions (5%, 10%, and 15%) were used to fertilize channel catfish eggs from three females. Fertilization ranged from 24% to 97%, and no difference in fertilization success was found between cryopreserved sperm and untreated sperm from the same males. Growth of channel ...

Multispecies hybridization among native and introduced centrarchid basses in central Texas.

Abstract Allele-frequency differences at 11 polymorphic protein loci provided discrete genetic markers with which to estimate the extent of hybridization among native and introduced centrarchid basses in central Texas streams. Native Guadalupe bass Micropterus treculi and northern largemouth bass M. salmoides salmoides now coexist with introduced Florida largemouth bass M. s. floridanus and smallmouth bass M. dolomieui in these streams. Interspecific hybridization was detected in three of four populations from the Blanco and San Marcos rivers, hybrids making up at least 31.8% of the individuals sampled. Complex hybridization patterns were evident, because F1, F2, and backcross hybrids were detected. At least one individual exhibited genetic markers of largemouth, smallmouth, and Guadalupe bass. Extensive multispecies hybridization threatens the survival of the endemic Guadalupe bass.

Influence of dihydrotestosterone on sex determination in channel catfish and blue catfish: Period of developmental sensitivity

Treatment of channel catfish with 0.2, 20, or 200 mg/liter of dihydrotestosterone (DHT) in the water during the egg stage or during egg and sac-fry stages did not alter the expected 1:1 sex ratio of the progeny. Feeding DHT at 200 mg/kg of feed for the first 21 days after yolk sac absorption resulted in 80% females; this proportion was increased by combining feeding with treatment of 200 mg DHT/liter in the sac-fry stage (90%) or in the egg and sac-fry stage (97%). In contrast, treatment of blue catfish sac-fry with 200 mg DHT/liter, with or without the combination of feeding DHT at 200 mg/kg food, resulted in 100% female populations. Neither clomiphene citrate, an estrogen-receptor blocking agent, nor clofibrate, an inhibitor of hepatic synthesis of cholesterol, affected the sex ratio of channel catfish, and neither of these compounds altered the feminizing effect of 200 mg DHT/kg when fed in combination with DHT. The nonaromatizable androgen DHT is not as effective as many other androgens in producing paradoxical female populations of channel catfish. However, feminization of blue catfish by treatment of sac-fry indicates that this species is more susceptible to hormonal manipulation and that the period of sex determination may occur earlier in development than in channel catfish.

Stability of genome size among stocks of the channel catfish

Abstract Nuclear DNA content of erythrocytes from male and female channel catfish ( Ictalurus punctatus ) was determined by flow cytometry. Fourteen stocks of catfish were studied ( n =115), including domesticated and wild fish, fish from sex-reversed populations and those produced by gynogenesis. Mean DNA content was 1.977±0.010 (SD) pg DNA per cell, and mean within-stock variation was 1.28%. The stocks had an average difference of 0.19% from the species mean; no significant differences in DNA content were detected among the stocks or between males and females. The intraspecific variation among the channel catfish stocks examined is lower than that reported for other fish species. This may reflect artificial stabilization of genome size by human intervention, or alternatively, evolutionary conservatism within the genome of the channel catfish.

Growth of channel catfish in mixed sex and monosex pond culture

Abstract Growth of male and female channel catfish ( Ictalurus punctatus ) was monitored for 6 months in triplicate 0.04-ha ponds (7500 fish/ha) stocked with mixed sexes (60–65% male), monosex males (90–98% male) or monosex females (98–100% female). Average weight and length and total weight were not different among treatment groups at any of the monthly samples. Harvest size of males was similar in ponds stocked with mixed sexes (mean±s.e.; 579±10 g and 324±2 mm, n =184), monosex males (596±9 g and 326±2 mm, n =282) and monosex females (607±48 g and 333±6 mm, n =3), parallel to the pattern observed for females in ponds stocked with mixed sexes (474±10 g and 305±2 mm, n =116), monosex males (458±21 g and 302±5 mm, n =18) and monosex females (494±7 g and 311±1 mm, n =297). Males were significantly heavier and longer than females in ponds with mixed sexes and with monosex males, but females and the small number of males in monosex female ponds were not statistically different in size. Feed conversion efficiencies were similar among treatment groups at each monthly sample, but the overall average for ponds with monosex males (0.743±0.01) was significantly higher than ponds with mixed sexes (0.670±0.02) and monosex females (0.676±0.01). Intrinsic growth patterns for both sexes were retained in monosex and mixed sex culture, demonstrating that the superior growth of males has a genetic component and is not due simply to more aggressive feeding behavior. The average weight of channel catfish harvested from monosex male ponds was about 8.5% higher than fish in mixed sex ponds and 15% higher than fish in monosex female ponds, suggesting that culture of monosex male channel catfish could provide an economic benefit.

Electrophoretic Identification of Genetic Markers in Channel Catfish and Blue Catfish by Use of Low-Risk Tissues

Abstract Electrophoretic analysis of enzymes and proteins enables aquaculturists to distinguish among stocks of channel catfish Ictalurus punctatus and blue catfish I. furcatus, and to monitor gene flow, hybridization, and inbreeding. Sixteen previously unreported genetic markers allow much more precise resolution of stock differences. Analysis of low-risk tissue samples (caudal fin, adipose fin, and barbels) enables investigators to obtain genetic data with little stress on individual fish. We have identified at least 69 enzyme locus products in populations of channel catfish (Kansas, Marion, “Auburn,” Mississippi, and Red River strains) and blue catfish by use of autopsied tissues. Polymorphic loci account for at least 36% of the loci examined. Allelic polymorphisms fixed between blue and channel catfish were observed at 13 loci. Genetic variation was observed at 17 loci among channel catfish populations and at 5 loci in the single blue catfish population. Analysis of species-specific genetic markers am...

Differential Resistance among Channel Catfish Strains and Intraspecific Hybrids to Environmental Nitrite

Abstract Fifteen strains and intraspecific hybrids of channel catfish Ictalurus punctatus were exposed to 76–79 mg nitrite-N/L. After 48 h of exposure, a significant difference (P = 0.0092) was observed in the number of dead fish among groups. The existence of nitrite-resistant and nitrite-susceptible strains of channel catfish provides another management criterion for aquaculturists in localities where nitrite toxicosis is a problem, and perhaps provides a basis for the development of a more nitrite-resistant aquaculture stock.

Recovery of Channel Catfish from Abdominal Surgery

Abstract Surgical incisions, performed with anesthesia in a septic environment, were made in the lateral–ventral abdominal wall of 244 fingerling channel catfish (Ictalurus punetatus; mean weight, 39.8 g ± 1.2 SE), and survival was monitored for 27 d. The incisions allowed gross observation of developing gonads to determine gender. After fish recovered from anesthesia in aerated water (about 30 min after they were first netted), they were dosed with NaCl (5.9 g/L) and nitrofurazone (211 mg/L). Thereafter, the fish were treated twice daily for 10 d with salt and nitrofurazone in a flow-through water system. They resumed feeding 6 d after surgery. Twenty-seven days after surgery, survival averaged 95.5% and all incisions were healed. Small channel catfish do not have to be killed or allowed to die after invasive procedures. Nevertheless, continued research is needed on noninvasive procedures to obtain biological information without surgery-related mortality.

Size Grading May Alter Sex Ratios of Fingerling Channel Catfish

The influence of size grading on sex ratios and growth was evaluated for small (0.2- 4.0 g) channel catfish (Ictalurus punctatus). Channel catfish from 15 families were ungraded or were graded into two or three size-groups by mean of bar graders with 0.40-0.99-cm slot widths. The 57 groups obtained were reared separately for 3-4 months in 150-L fiberglass tanks. Weight, length, and sex were then determined on up to 100 fish per group. The frequency of males from all families was 51.5%: although progeny from individual families varied from 45.1 to 56.0% males, the frequencies were not different from the expected 1:1 male: female ratio. Males usually were preferentially selected (mean ± SD, 65.1 ± 3.5%) by a grader with a slot width of 0.91 cm, which retained the largest fish in a population; graders with smaller slot widths did not consistently affect the sex distribution. Harvest size of finger lings was variable and was influenced by initial weights and densities; family-by-grader interactions were significant (P s 0.05). Sexually dimorphic growth was observed in 19 of 57 tanks, and in those instances males were always larger than females. Variances for weight and length between sexes were different in less than 10% of the tanks, and the magnitude of the variance differences was significantly influenced by families. These results suggest that grading fingerlings as small as 3 g can affect sex ratios and that channel catfish families may be selected to enhance or decrease sex-related growth differences.