Martin S. Fitzpatrick

Effects of stress on fish reproduction, gamete quality, and progeny☆

Different taxa of fish have different tolerances to stress. This implies that for a particular stressor, severity may vary depending on the species to which it was applied. Species may differ in the nature of their physiological response and reproductive consequences to stressors. For example, disturbance or handling may affect the timing of reproduction—accelerating or delaying it as the case may be—in species such as rainbow trout (Oncorhynchus mykiss); however, tilapia (Oreochromis niloticus) respond by acceleration or complete inhibition of reproduction, depending on the maturational stage when the stressor is experienced. Strategies for coping with stress affect reproductive fitness either in terms of gamete or progeny quality. The physiology associated with maturation and spawning appears tightly coupled with stress physiology. Environmental variables, particularly nutrition, are ultimately important in affecting gamete quality and reproductive timing. The physiological response to stressors is also quite polymorphic, within and between species. For example, the circulating concentration of the primary stress response factor cortisol varies greatly among resting and among stressed rainbow trout stocks. Immunocapacity can be influenced by stress, reducing reproductive fitness of broodfish. We propose that maternal systems have been developed to buffer eggs from deleterious consequences of stressors, including regulation of transfer of substances of maternal origin to the egg and in mechanisms controlling the timing of reproduction. Effects of nutritional stressors are moderated by effects on timing of first maturity or subsequent reproductive events and/or by maintenance of quality of some eggs via atresia of others. Deleterious overload of eggs with substances such as cortisol is likely prevented by limiting entry of these compounds into the eggs. Barriers to vertical transmission of numerous pathogens seem to exist, while maternally derived immune protection is provided to assist with disease prevention of pathogenic organisms acquired from parents or by direct post-spawning infection. Timing of reproductive events including puberty, atresia, maturation and ovulation are influenced by other physiological variables responsive to stressors. Knowledge of how a stressor might affect the physiology of a species can help in development of management tactics that lessen the impact of a stressor or even in the development of therapeutants. Published by Elsevier Science B.V.

The Ecological and Cultural Importance of a Species at Risk of Extinction, Pacific Lamprey

Abstract The cultural and ecological values of Pacific lamprey (Lampetra tridentata) have not been understood by Euro-Americans and thus their great decline has almost gone unnoticed except by Native Americans, who elevated the issue and initiated research to restore its populations, at least in the Columbia Basin. They regard Pacific lamprey as a highly valued resource and as a result ksuyas (lamprey) has become one of their cultural icons. Ksuyas are harvested to this day as a subsistence food by various tribes along the Pacific coast and are highly regarded for their cultural value. Interestingly, our review suggests that the Pacific lamprey plays an important role in the food web, may have acted as a buffer for salmon from predators, and may have been an important source of marine nutrients to oligotrophic watersheds. This is very different from the Euro-American perception that lampreys are pests. We suggest that cultural biases affected management policies.

Cloning of a second proopiomelanocortin cDNA from the pituitary of the sturgeon, Acipenser transmontanus.

A recent study on the pituitary of the sturgeon, Acipenser transmontanus, resulted in the cloning of a cDNA that codes for the prohormone, proopiomelanocortin (POMC). This cDNA is designated sturgeon POMC A. Subsequent analysis of the sturgeon pituitary uncovered a second distinct POMC cDNA (sturgeon POMC B). In both sturgeon POMC cDNAs the open reading frame is 795 nucleotides in length. However, the two sturgeon POMC cDNAs differ at 26 amino acid positions in the opening frame. In addition, the 2 forms of POMC differ at 45 nucleotide positions within the open reading frame. The number and types of point mutations are compared in the 2 sturgeons POMC cDNAs, and the origin of the two POMC genes is discussed.

Effects of thermal regime on ovarian maturation and plasma sex steroids in farmed white sturgeon, Acipenser transmontanus

Abstract Recently, commercial aquaculture farms in Northern California have exposed gravid, cultured white sturgeon females to cold water (12±1°C) throughout the late phase of vitellogenesis and ovarian follicle maturation resulting in improved ovulation rates and egg quality. However, the optimum timing for transfer of broodfish to the cold water and the capacity of transferred broodfish to maintain reproductive competence over an extended time in cold water had not been evaluated. Gravid white sturgeon females that have been raised at water temperatures of 16–20°C were transported to either cold water (12±1°C; Group 1) in November 1997 or maintained in ambient water temperatures (10–19°C; Group 2) until early spring. In March 1998, half of the fish in Group 2 had regressed ovaries, but the remaining females had intact ovarian follicles and were transported to the cold water. Ovarian follicles and blood were collected from females until they reached the stage of spawning readiness (determined by germinal vesicle position and an oocyte maturation assay) or underwent ovarian regression. Exposure of gravid sturgeon females to ambient water temperatures (14.5±2.3°C, mean±S.D.) from October to March led to a decrease in plasma sex steroids and a high incidence of ovarian regression in fish with a more advanced stage of oocyte development. Transfer of females with intact ovarian follicles to cold water (12±1°C) in the fall or early spring resulted in normal ovarian development in the majority of females. Holding females in cold water does not seem to override their endogenous reproductive rhythms but extends their capacity to maintain oocyte maturational competence over a longer period of time. A temperature-sensitive phase in ovarian development may occur during the transition from vitellogenic growth to oocyte maturation, and the degree and timing of sensitivity to environmental temperature are dependent on the females endogenous reproductive rhythm.

Regulation of the interrenal of fishes: non-classical control mechanisms

The regulation of the interrenal of teleostean fishes is reviewed from the perspective of non-classical control mechanisms and new evidence is presented suggesting gonadotropic control of the interrenal. Cortisol secretion by the interrenal, in addition to regulation by ACTH, appears to be mediated by other hormones. Physiologically relevant, direct control of interrenal function by hydromineral factors is unclear.In vitro experiments with interrenals of coho salmon (Oncorhynchus kisutch) indicate that salmon gonadotropin is extremely corticotropic and both ACTH and gonadotropin stimulate the secretion of large quantities of androstenedione from the interrenal.

Evidence for ultra-short-loop feedback in ACTH-induced interrenal steroidogenesis in coho salmon: acute self-suppression of cortisol secretion in vitro.

Interrenal tissues from coho salmon (Oncorhynchus kisutch) were incubated in a defined medium under blood-gas atmosphere at 17 degrees. Rates of cortisol secretion by tissues incubated in media containing 50 mU/ml porcine-ACTH were initially much greater than those of resting tissues in hormone-free media, but after 3 to 6 hr returned to resting rates. The time course of cortisol accumulation in ACTH-containing media was the same when tissues were incubated in different volumes; the final concentrations of cortisol in these incubations were similar to each other and resembled peak in vivo concentrations in juvenile coho subjected to acute stress. Cortisol secretion rates of tissues sequentially transferred to fresh ACTH-containing media every 6 hr did not return to resting levels but remained elevated for at least 24 hr. Cortisol secretion in response to ACTH was attenuated or completely abolished in tissues incubated in media containing exogenous cortisol; this effect was reversible and dose-dependent. Our results suggest that in coho salmon, cortisol may exert ultra-short-loop negative feedback directly at the level of the interrenal gland to effect self-suppression.

Identification and Enumeration of Steelhead Kelts at a Snake River Hydroelectric Dam

Abstract Improvement of iteroparity rates in U.S. Endangered Species Act (ESA)-listed Snake River populations of steelhead Oncorhynchus mykiss requires a means of distinguishing prespawn (mature) steelhead from postspawners (kelts) and sufficient kelt abundance to aid recovery efforts. We used ultrasound imaging of gonads to identify and enumerate prespawn steelhead and kelts incidentally collected in the juvenile bypass facility at Lower Granite Dam (LGR) on the Snake River, Washington. We also evaluated the accuracy of visual identifications based on external coloration and condition in relation to the known maturational status determined by ultrasound examinations. Steelhead (n = 1,353) were sampled during 10 weeks between April and June 2000, a period that spanned the peak of adult steelhead occurrence in the juvenile bypass system. Based on ultrasound appraisals, we estimated that kelts composed 94.6% of the 3,968 adult steelhead encountered in the LGR juvenile bypass system during the study period. ...

Morpho-physiological predictors of ovulatory success in white sturgeon, Acipenser transmontanus Richardson

Abstract Body length, oocyte diameter, germinal vesicle position, in vitro oocyte maturation response to progesterone, and plasma concentrations of progesterone, cortocosteroids, and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHP) were examined in white sturgeon females prior to their spawning induction and correlated with their subsequent ovulatory response. The relationship between broodfish size and ovulatory success was insignificant. Responsive females had larger oocytes and elevated plasma concentrations of corticosteroids and 17α,20β-diOHP, but did not differ significantly from nonresponsive females in progesterone concentrations. Germinal vesicle position and in vitro oocyte maturation response exhibited the closest relationships with ovulation, and can be used as practical predictors of ovulation for hormonally induced spawning of white sturgeon.

In vitro detection of functional humoral immunocompetence in juvenile chinook salmon (Oncorhynchus tshawytscha) using flow cytometry

A flow cytometric (FCM) assay for detection of immunomodulatory effects of environmental factors on the humoral response of chinook salmon (Oncorhynchus tshawytscha) is described and validated. This technique combines exposure of whole animals or leucocyte cultures to immunomodulatory agents/conditions with in vitro mitogenic activation of B-lymphocytes. The proportion of leucocytes undergoing blastogenesis following in vitro stimulation with lipopolysaccharide (LPS) is quantified by FCM analysis of forward and side scatter properties. In addition, binding of a fluorescein isothiocyanate labelled anti-rainbow trout immunoglobulin M monoclonal antibody (anti-RBT SIgM-FITC), quantified by FCM analysis, is used to determine the ability of the lymphoblasts to express surface immunoglobulin M (SIgM). Through a series of calibration steps, it was confirmed that anti-RBT IgM-FITC was specific for B-lymphocyte SIgM in chinook salmon. Binding of anti-RBT IgM-FITC to chinook salmon SIgM positive leucocytes was effectively blocked with salmon serum and an isotype control was established. B-lymphocytes were partially removed from a population of leucocytes through adherence to a nylon wool column, which then demonstrated a consequent reduction in anti-RBT IgM-FITC binding. Using anti-RBT IgM-FITC as a marker, the distribution of resting lymphocytes expressing SIgM in lymphoid tissues of juvenile chinook salmon was described. The mean percentage of SIgM positive cells in spleen, pronephros and blood were found to be 62.1 (+/-2.82), 34.8 (+/-1.86) and 56.7% (+/-4.7) of all viable leucocytes, respectively. In a time-course experiment for optimal in vitro activation of leucocytes for this assay, blastogenesis and up-regulation of SIgM expression of splenic leucocytes were observed through FCM by 4 days post in vitro stimulation with LPS, continued through 7 days, but was no longer visible by 10 days post stimulation. Using this assay, reduced expression of SIgM in splenic and pronephric B-lymphocytes was detected following in vitro exposure to physiologically relevant stress concentrations of cortisol in conjunction with mitogenic stimulation. This technique will be a useful addition to the assays already available in the rapidly growing field of fish immunology.

Technical Notes: Evaluation of Three Candidate Fungicides for Treatment of Adult Spring Chinook Salmon

Abstract Use of malachite green as a fungicide in fish culture was terminated by the U.S. Food and Drug Administration (FDA) in 1991. Formalin has been the replacement antifungal agent, but the present FDA registration restricts its use to only eggs of salmonids and esocids: further, concerns about its safety for users and about formalin effluents in the environment persist. Three candidate chemicals (iodine, glutaraldehyde, and hydrogen peroxide) were tested along with the reference fungicides malachite green and formalin for antifungal activity on adult spring chinook salmon (Oncorhynchus tshawytscha). Compounds were added to flow-through systems without correction for flow dilution. Malachite green and formalin were effective in preventing prespawning mortality and in minimizing the incidence of fungal infection. Fish from iodine treatments at 0.1 or 0.02 mg/L had mortality levels like those of untreated controls. Most deaths of iodine-treated (and control) fish were accompanied by fungal infections, w...