Kenneth B. Davis

Characterization and Alleviation of Stress Associated with Hauling Largemouth Bass

Abstract Stress and mortality associated with truck transport of largemouth bass Micropterus salmoides were characterized during and after simulated hauling periods of up to 30 hours at a density of 180 g fish/liter of water. Generally, “transported” fish had significantly elevated concentrations of plasma glucose and corticosteroids and decreased plasma chloride concentrations and osmolality. Significant mortality was associated with hauls of 24 and 30 hours (38% and 83–92%, respectively). Plasma characteristics returned to near-normal values 3–28 days after being hauled; recovery time generally was related to length of haul and associated mortality. Stress was reduced significantly and mortality was eliminated when fish were treated for diseases, held 72 hours without food before they were loaded, anesthetized before they were loaded, hauled at a cool temperature in physiological concentrations of salts with an antibiotic and a mild anesthetic, and allowed to recover in the same medium less the anesthet...

SEX DIFFERENTIATION OF CHANNEL CATFISH GONADS : NORMAL DEVELOPMENT AND EFFECTS OF TEMPERATURE

Channel catfish have an XX female-XY male sex determination system. Although genetic males of this species are readily feminized with exogenous steroid, the pattern of gonadal sex differentiation and the effect of temperature on genetic sex determination are unknown. To document the pattern of gonadal sex differentiation, catfish from a mixed-sex progeny (XX female-XY made cross), known XY males (XX female-YY male cross), and steroid sex-reversed (XY) females were reared at 28°C and collected for histological analysis from Day 7 to Day 90 postfertilization. No signs of gonadal sex differentiation were detected from Day 7 to Day 16. On Day 19, about half the fish from the mixed-sex population as well as the sex-reversed females had gonads with proximal and distal tissue outgrowths. These outgrowths eventually fused to form an ovarian cavity. Germ cell meiosis in these gonads was first detected on Day 22 and growing ovarian follicles were seen at later stages. Thus, ovarian differentiation began about Day 19. Although presumptive testes lose their sensitivity to feminizing steroids about Day 19, the gonads of known males and of putative males from the mixed-sex population showed no clear signs of sex differentiation up to Day 90. Thus, the prolonged temporal dissociation between testicular commitment and differentiation indicates that these two events may be mediated by separate stimuli. To determine the effects of temperature on sex determination, fish of a mixed-sex population were reared at 27°C until Day 10; at 20°, 27°, or 34°C from Day 10 to Day 24; and then at 27°C until Day 102 when sex ratios and gonadal histology were determined. The sex ratio was significantly skewed toward females in fish treated at 34°C (1 male:1.68 female; P < 0.01) but no effects were seen at 20° or 27°C. This observation suggests that genetic and temperature-dependent mechanisms of sex determination are both functional in channel catfish and that this phenomenon is more widespread in fishes than previously believed. The testes of the Day 102 males examined had developed positive histological signs of sex differentiation, suggesting that testicular formation in channel catfish normally starts between Day 90 and 102.

Confinement and water quality-induced stress in largemouth bass

Abstract Plasma values of corticosteroids, glucose, chloride, and osmolality were determined in largemouth bass Micropterus salmoides under various environmental conditions. No differences were observed in quiescent fish due to sex, size, time of day, or the types of holding facilities tested (tanks, raceways, ponds). Differences were observed in plasma glucose, chloride, and osmolality values among fish acclimated to 10, 16, and 23 C. Abrupt temperature changes caused elevations in plasma corticosteroid and glucose concentrations and reduced plasma chloride and osmolality. Confinement in a net, for up to 48 hours, caused elevated glucose and corticosteroids and reduced chloride and osmolality values. After 48 hours of confinement, fish required up to 14 days to recover normal plasma characters. Generally, short-term exposure to poor water quality (high concentrations of CO2 and NH3, and low concentrations of dissolved oxygen) altered plasma corticosteroids and glucose but had little effect on plasma chlo...

Effects of Environmental pH and Calcium on Ammonia Toxicity in Channel Catfish

Abstract The twenty-four-hour median lethal concentrations (24-hour LC50) of total ammonia nitrogen (TA-N) to channel catfish (Ictalurus punctatus) at pH 7, 8, and 9 (total hardness, 40 mg/liter; temperature, 21–25 C) were 263.6 ± 11.3 (SE), 38.8 ± 1.8, and 4.5 ± 0.2 mg/liter, respectively. The 24-hour LC50 of un-ionized ammonia nitrogen (UIA-N) concentration at pH 8 was significantly higher (1.82 ± 0.06 mg/liter) than at pH 7 or 9 (1.39 ± 0.06 and 1.49 ± 0.12 mg/liter). Enrichment of the water to 440 mg/liter 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/liter 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/liter TA-N at pH 8. No differences in blood pH were found betwee...

Physiological stress in striped bass : effect of acclimation temperature

Abstract Physiological responses to acclimation temperature and confinement stress were studied in yearling striped bass, Morone saxatilis . Temperature significantly affected plasma cortisol, glucose, chloride, and hematocrit but not osmolality in fish acclimated to 5, 10, 16, 21, 25 and 30°C. Close confinement for 12 min in a net resulted in changes of these characteristics in some or all of these groups. Generally, plasma cortisol and glucose increased, and plasma chloride, osmolality, and hematocrit decreased due to net confinement, and returned toward resting levels after release from the net. The physiological changes during stress were greatest and the recovery from these changes was slowest at 5 and 30°C. Further, the quantitative response was least and the recovery most rapid in fish stressed at 10 and 16°C. Acclimating and moving striped bass within this temperature range should decrease stress-related responses and mortality and thus improve yield after stocking.

Effect of handling stress on susceptibility of channel catfish Ictalurus punctatus to Ichthyophthirius multifiliis and channel catfish virus infection

A quantitative bioassay employing immersion exposure was developed for the infection of channel catfish Ictalurus punctatus with the protozoan parasite Ichthyophthirius multifiliis, commonly referred to as ich. This bioassay as well as waterborne challenge of channel catfish with channel catfish virus (CCV) was used to investigate the effect of confinement stress on the sensitivity of the fish to exposure of these pathogens. Infestation by ich was shown to be proportional to the density of infective theronts in the exposure tank and low-water crowding stress was shown to increase susceptibility of catfish to infection. Mortality from CCV was related to the virus exposure dose; however, low-water crowding stress did not affect mortality. Increased susceptibility, due to crowding stress of naive channel catfish to I. multifiliis but not to CCV, suggests a difference in the defence mechanisms. Stress-induced increased susceptibility to I. multifiliis may be due to a suppression of an innate protection mechanism. The lack of effect of stress on CCV mortality may be due to protection afforded by an inducible system which was not affected by the stressor, or the lethal effects of the virus were too fast for the stress to change susceptibility in fish exposed to CCV for the first time.

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.

Feminization of Channel Catfish by Oral Administration of Steroid Sex Hormones

Abstract Oral administration of 17-β-estradiol or 17-α-ethynyltestosterone to sexually undifferentiated channel catfish Ictaturus punctatus during the first 21 days after yolk-sac absorption resulted in the production of 100% females. The androgen was effective at doses of 6 to 600 μg/g of feed, but not at 0.6 μg/g. Received February 5, 1983 Accepted June 12, 1983

Management of Physiological Stress in Finfish Aquaculture

Abstract Physiological stress is a nonspecific response common to all vertebrate organisms initiated by many types of environmental changes. Stress in fish can be characterized by physiological changes such as plasma cortisol, glucose, lactate, and electrolyte concentrations and is quantitatively related to the severity and longevity of the stressor. A hierarchy is evident among the physiological changes, such that adrenalin from activation of the sympathetic nervous system is released most rapidly, followed by cortisol, and then glucose. Plasma electrolyte disturbances may not occur until the stress is severe and present for an extended time. Adrenalin increases plasma glucose by stimulating liver glycogenolysis, which represents a metabolic energy cost to the fish. The functions of cortisol include possible induction of gluconeogenesis and suppression of the inflammatory response. Maintaining osmoregulatory homeostasis is an energetically expensive process, and disturbances deplete energy reserves. Rece...

Hormonal sex manipulation and evidence for female homogamety in channel catfish

The mechanism of sex determination in channel catfish Ictalurus punctatus was evaluated by hormonal and genetic methods. Aromatizable and nonaromatizable androgens, as well as an estrogen, caused feminization in fish fed steroids for 21 days after yolk-sac absorption. The effectiveness of 60 micrograms of ethynyltestosterone/g food decreased markedly when the experimental feeding period was shortened and was ineffective when the treatment lasted less than 12 days. Females from all-female populations produced by treatment with sex hormones were mated with normal males resulting in nine spawns with a sex ratio different from 1:1. The sex ratios were statistically similar to 3 male: 1 female in five spawns, both 2:1 and 3:1 in two spawns, and 2:1 in two spawns. These data are consistent with a model for female homogametic sex determination in channel catfish and suggest that the YY equivalent genotype is viable.