Cheryl A. Goudie

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 ...

Production of gynogenetic and polyploid catfish by pressure-induced chromosome set manipulation

Channel catfish (Ictalurus punctatus) eggs fertilized with sperm from blue catfish (I. furcatus) or channel catfish (60 or 90 s UV-irradiated, 0.08 or 0.12 J/cm2, respectively; 20–30% motility) were subjected to early hydrostatic pressure (5 min post-fertilization; 8000 psi; 3 min duration) to produce meiotic gynogens or late hydrostatic pressure (90 min post-fertilization) to produce mitotic gynogens. Polyploid hybrid catfish (I. punctatus X I. furcatus) were produced using eggs fertilized with untreated sperm followed by pressure treatments. Eggs fertilized with irradiated sperm (putative haploids) exhibited slow and abnormal development, and did not survive to hatch. Pressure treatments reduced the frequency of normal development at blastula, neurula and tailbud stages compared with stripped controls. Relative survival at 1.5 months was 2% for meiotic and 0.2% for mitotic gynogens, and 66% for triploid and 8% for tetraploid groups, compared with 27% survival of stripped controls. Sex ratios varied among families in hybrid groups but averaged close to 1:1 male:female, whereas offspring in gynogenetic families were all female. Particle size analysis of erythrocyte nuclear volumes indicated 91–100% triploidy induction, but only 4% tetraploidy induction. Although the numbers of gynogenetic channel catfish produced were small, the more than 500 viable offspring surviving represent foundation broodstock to facilitate genetic improvement strategies in this commercially important species.

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.

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.

Sex-linkage of glucosephosphate isomerase-B and mapping of the sex-determining gene in channel catfish

Sex-linkage of glucosephosphate isomerase-B (GPI-B) was observed in five experimental matings between heterozygous male and homozygous female channel catfish (Ictalurus punctatus). Offspring phenotypes for GPI-B were 40.8% heterozygous male and 43.0% homozygous female, while recombinant offspring were 7.4% homozygous male and 8.8% heterozygous female. Thus, GPI-B and the sex-determining gene (SDG) were linked and had a recombination rate of 16.2%. This linkage was designated I. punctatus linkage group XXIX. The gene-centromere distance (1.66 cM) of SDG, estimated in six gynogenetic families derived from XY females, indicated that SDG resides very close to the centromere. Based on estimates of these genetic distances, a chromosomal order of GPI-B-centromere-SDG was proposed. Additionally, joint segregation of GPI-A and SDG in two experimental matings indicated no genetic linkage between GPI-A and sex. These genetic relationships were compared to those reported in other teleost taxa with regard to evolutionary conservation of ancestral gene arrangements.

GENETIC RELATIONSHIP OF GROWTH, SEX AND GLUCOSEPHOSPHATE ISOMERASE-B PHENOTYPES IN CHANNEL CATFISH (ICTALURUS PUNCTATUS)

Abstract Growth of fish has been associated with the phenotypes of specific biochemical genetic loci, although the correlation of growth with sex-specific loci has not been routinely studied. In a previous study in channel catfish ( Ictalurus punctatus ), glucose phosphate isomerase-B (GPI-B) was linked with the sex-determining gene (SDG) with a recombination frequency of 15.2%. Growth performance related to sex and GPI-B phenotypes was investigated in five experimental matings of channel catfish. The association of sex and GPI-B with growth, differences in growth among GPI-B phenotypes, and the degree of linkage with growth between sex and GPI-B were evaluated by ANOVA followed by Duncans Multiple Range Test ( P

Isozyme Expression and Gene–Centromere Distances in Diploid and Triploid Hybrid Catfish

Abstract Allozyme expression of 14 loci was studied in diploid channel catfish Ictalurus punctatus, blue catfish I. furcatus, and diploid and triploid hybrid catfish (channel catfish × blue catfish). This allowed appropriate interpretation of allozyme expression and estimates of gene–centromere distances in triploid hybrid catfish and contributed to genetic characterization of the commercially important ictalurid catfishes. Five polymorphic loci in the parental female channel catfish were used to confirm the retention of an extra diagnostic maternal allele in triploid offspring. Fidelity of gene dosage and allozyme expression of three parental alleles were found at 13 of 14 loci of triploid progeny; however, expression of phosphoglucomutase (PGM) in 174 and 197 triploid hybrids was similar to that of diploid hybrids. Electrophoretic variation for PGM was observed when different buffers were used, indicating nongenetic alteration of expression. Two polymorphic loci in triploid hybrid catfish provided new g...

Sex Genotype and Sex Phenotype Contribute to Growth Differences between Male and Female Channel Catfish

Abstract Channel catfish Ictalurus punctatus have an XX female-XY male genotypic system of sex determination, and male channel catfish grow faster than females. Through selective breeding and appropriately timed hormone administration, we have produced phenotypic male channel catfish with a YY sex genotype and female channel catfish with an XY or YY sex genotype. In this study, we evaluated the relative role of sex genotype and sex phenotype in regulating sexually dimorphic growth in this important aquaculture species. Ten families of genotypic XY male fish were produced by matings of normal XX female fish with YY male fish, and females were produced by hormonal feminization of a subsample from each family. The growth rate and body composition of sibling males and females in ponds where the sexes were maintained together were compared with those in ponds where the sexes were maintained separately. Generally, phenotypic males had higher body weight (15.25% and 11.36% when the sexes were together or separat...

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.