Sex genotype and sex phenotype contribute to growth differences between male and female channel catfish

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 separated, respectively), standard length (3.28% and 2.24%, respectively), and condition factor (2.94 and 2.65, respectively), while phenotypic females had higher liposomatic index (7.11% and 13.69%, respectively) and dress-out percentage (0.91% and 1.06%, respectively). Statistical differences between the phenotypic sexes were not as consistent as observed in previous studies with normal males and females because growth and body composition differences were enhanced when the sexes were maintained together; however, monosex culture restrained these differences. These results demonstrate that sex genotype and sex phenotype both contribute to the male growth advantage in channel catfish and provide further evidence that monosex male culture would produce an economic gain of about 5% for the industry compared with conventional mixed-sex culture. © Copyright by the American Fisheries Society 2007

Effects of environmental pH and calcium on ammonia toxicity in channel catfish

The 24-hour median lethal concentrations (24-hour LC50) of total ammonia nitrogen (TA-N) to channel catfish (Ictalarus punctatus) at pH 7, 8, and 9 (total hardness, 40 mg/l; temperature, 21-25 C) were 263.6 ± 11.3 (SE), 38.8 ± 1.8, and 4.5 ± 0.2 mg/l, respectively. The 24-hour LC50 of un-ionized ammonia nitrogen (UIA-N) concentration at pH 8 was significantly higher (1.82 ± 0.06 mg/l) than at pH 7 or 9 (1.39 ± 0.06 and 1.49 ± 0.12 mg/l). Enrichment of the water to 440 mg/l total hardness at pH 7 significantly increased the 24-hour LC50 of TA-N and UIA-N (356.3 ± 16.4 and 1.79 ± 0.07). Fish exposed to 25 mg/l TA-N for 12 hours at pH 7 and 8 showed no differences from control fish in hematocrit percent total plasma protein, or plasma and muscle chloride. Plasma sodium showed no difference between control and experimental groups at pH 7: however, a significant decrease occurred in fish exposed to 25 mg/l TA-N at pH 8. No differences in blood pH were found between the control groups and fish exposed to 100 and 200 mg/l TA-N at pH 7, and to 10 and 25 mg/l TA-N at pH 8. Plasma sodium depletion is suggested as a contributing mechanism of ammonia toxicity

Growth of channel catfish in mixed sex and monosex pond culture

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. © 1994

Survival, growth, and feed utilization of pre- and postmetamorphic American shad exposed to increasing salinity

The American shad Alosa sapidissima is currently an emerging aquaculture species in China, and establishing conditions required for optimal growth will play a key role in future development of American shad culture. We evaluated the effects of increasing salinity concentrations on survival, growth, and feed utilization of American shad in two separate 30-d experiments. In experiment 1, 25-d-old, premetamorphic fish (mean weight ± SD =0.07 ± 0.04 g) were exposed to 0, 10, 20, and 30-ppt salinity (26-29°C). In experiment 2, 80-d-old, postmetamorphic fish (1.46 ± 0.52 g) were exposed to 0, 5, 10, 20, and 30-ppt salinity (21-26°C). Mortality was markedly higher at salinities of 20 ppt (52% and 74%, respectively, for pre- and postmetamorphic fish) and 30 ppt (100% and 90%, respectively) than at 0 and 5 ppt (<1%). Specific growth rate (SGR) and feed conversion efficiency (FCE) were highest at 0-ppt salinity for premetamorphic fish (SGR =8.81% per day; FCE =1.12) and at 5-ppt salinity for postmetamorphic fish (SGR =4.59% per day; FCE =0.87). The SGR and FCE were lowest at 30-ppt salinity, and a significant negative relationship was demonstrated between salinity and SGR and between salinity and FCE. In both experiments, SGR and FCE were positively correlated. Our observations demonstrate that culture of young American shad may be possible at salinities up to 10 ppt, but 0-5-ppt salinity produced the best growth. © Copyright by the American Fisheries Society 2009

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

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. © 1995

Genetic relationship of growth, sex and glucosephosphate isomerase-B phenotypes in channel catfish (Ictalurus punctatus)

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 Duncan's Multiple Range Test (P < 0.05). Significant growth differences were found between males and females in all families examined; males outweighed females by 36%, confirming observations from earlier studies. The phenotypes of GPI-B were also associated with growth; however, heterozygotes at GPI-B exhibited higher relative weight than homozygotes only when the paternal parent was heterozygous, indicating that the heterozygosity of this allozyme did not directly induce the observed growth advantage. No growth advantage of heterozygosity in GPI-B was observed when recombination occurred between GPI-B and SDG; male and female recombinants had similar or lower relative weights compared to offspring with parental genotypes. These data indicate that sex is more tightly linked with growth-related gene(s) than GPI-B phenotypes, and no evidence supported direct involvement of GPI-B in growth of channel catfish. © 1995

Isozyme expression and gene-centromere distances in diploid and triploid hybrid catfish

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 X 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 gene-centromere distances of 14 centimorgans (cM) for aspartate aminotransferase (mAAT*) and 45 cM for glucose-6-phosphate isomerase (GPI-A*). No differences were found in recombination rates of isocitrate dehydrogenase (IDHP*) and peptidase-5 (PEPS-1*) loci of triploid hybrids at different ages. © Copyright by the American Fisheries Society 1996

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