Problems in the physiological monitoring of wild fish populations
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Environmental control of reproductive activity of captive fish is feasible (or potentially feasible) but, with few exceptions, is currently impractical for most species. Therefore, chemical methods of manipulating reproductive activity continue to be widely used in fish production operations worldwide. However, the control of fish reproduction in captivity cannot be exercised without regard to adequate environmental conditions, which can differ markedly for different species. This review provides a synopsis of relevant aspects of fish reproductive physiology and addresses current and promising future chemical methods of sex control, gonadal recrudescence, and spawning. Most research on the control of reproduction in fishes has focused on female physiology because ovarian development and maturation are easily disturbed by environmental stressors. Control of sex ratios by steroid treatment has become a well‐established technique for several fish species, but the technique continues to be problematic in some cases. Final gonadal growth and spawning usually can be achieved by implant treatment with gonadotropin‐releasing hormone analogs (GnRHa), which in some species have to be applied in combination with dopamine antagonists to enhance responsiveness to GnRHa. However, efforts to accelerate gonadal recrudescence and maturational competence by chemical means have yielded mixed results, reflecting a relative lack of understanding of the basic physiological and biochemical mechanisms controlling these processes. The potential benefits of using reproductive pheromones to manipulate gonadal development and spawning has been demonstrated in a few species, but further research is needed to determine whether this technique is applicable to fish culture. Because a reliable supply of young fish is critical for the expansion and diversification of fish culture operations, the use of chemicals in combination with adequate environmental conditions to control gametogenesis and spawning in fishes will continue to be an important tool for the fish culturist.
Typically, studies in digestive physiology in fish focus on a few enzymes and provide insight into the specific processes of the enzyme in a targeted species. Comparative studies assessing a wide number of digestive enzymes on fishes that compete for food resources are lacking, especially in the context of an introduced species. It is generally thought that the invasive silver carp (SVC; Hypophthalmichthys molitrix ) directly compete for food resources with the native gizzard shad (GZS; Dorosoma cepedianum ) in waters where they coexist. We compared 19 digestive enzymes between SVC and GZS throughout a year and in two rivers in the Midwestern United States: Illinois River and Wabash River. All digestive enzymes analyzed were detected in both SVC and GZS in both rivers. However, the profiles of the digestive enzymes varied by species. Alkaline phosphatase, valine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase and N-acetyl-β-glucosaminidase were all much higher in SVC than in GZS. Differences between digestive enzyme profiles were also observed between rivers and months. This study demonstrates the utility of using an ecological approach to compare physiological features in fishes.
Several experiments were performed to investigate the physiology of seawater acclimation in the striped bass, Morone saxatilis . Transfer of fish from fresh water (FW) to seawater (SW; 31–32 ppt) induced only a minimal disturbance of osmotic homeostasis. Ambient salinity did not affect plasma thyroxine, but plasma cortisol remained elevated for 24h after SW transfer. Gill and opercular membrane chloride cell density and Na + ,K + -ATPase activity were relatively high and unaffected by salinity. Average chloride cell size, however, was slightly increased (16%) in SW-acclimated fish. Gill succinate dehydrogenase activity was higher in SW-acclimated fish than in FW fish. Kidney Na + , K + -ATPase activity was slightly lower (16%) in SW fish than in FW fish. Posterior intestinal Na + ,K + -ATPase activity and water transport capacity (J v ) did not change upon SW transfer, whereas middle intestinal Na + ,K + -ATPase activity increased 35% after transfer and was correlated with an increase in J v (110%). As salinity induced only minor changes in the osmoregulatory organs examined, it is proposed that the intrinsic euryhalinity of the striped bass may be related to a high degree of “preparedness” for hypoosmoregulation that is uncommon among teleosts studied to data.
Populations of Pacific lamprey Lampetra tridentata have declined in the Columbia River basin. One factor that may have contributed to this reduction in population size is an excessive use of energy by adult lampreys as they negotiate fishways at dams during spawning migrations. To gain an understanding of the performance capacity of Pacific lampreys, we estimated the critical swimming speed (Ucrit) and documented physiological responses of radio-tagged and untagged adult lampreys exercised to exhaustion. The mean (??SD) Ucrit of untagged lampreys was 86.2 ?? 7.5 cm/s at 15??C, whereas the Ucrit for radio-tagged lampreys was 81.5 ?? 7.0 cm/s, a speed that was significantly lower than that of untagged fish. The physiological responses of tagged and untagged lampreys subjected to exhaustive exercise included decreases in blood pH of 0.3-0.5 units, a 40% decrease in muscle glycogen levels, a 22% increase in hematocrit for untagged fish only, and a 4- to 5-fold increase in muscle and a 40- to 100-fold increase in plasma lactate concentrations. These physiological changes were significant compared with resting control fish and usually returned to resting levels by 1-4 h after fatigue. Our estimates of Ucrit for Pacific lampreys are the first quantitative measures of their swimming performance and suggest that these fish may have difficulty negotiating fishways at dams on the Columbia River, which can have water velocities approaching 2 m/s. Our physiological results indicate that tagged and untagged Pacific lampreys show similar metabolic dysfunction after exhaustive exercise but recover quickly from a single exposure to such a stressor.
Simply and perhaps intuitively defined, endocrine disruption is the abnormal modulation of normal hormonal physiology by exogenous chemicals. In fish, endocrine disruption of the reproductive system has been observed worldwide in numerous species and is known to affect both males and females. Observations of biologically relevant endocrine disruption most commonly occurs near waste water treatment plant outfalls, pulp and paper mills, and areas of high organic loading sometimes associated with agricultural practices. Estrogenic endocrine disrupting chemicals (EEDCs) have received an overwhelmingly disproportionate amount of scientific attention compared to other EDCs in recent years. In male fishes, exposure to EEDCs can lead to the induction of testicular oocytes (intersex), measurable plasma vitellogenin protein, altered sex steroid profiles, abnormal spawning behavior, skewed population sex ratios, and lessened reproductive success. Interestingly, contemporary research purports that EDCs modulate aspects of non-reproductive physiology including immune function. Here we present an overview of endocrine disruption in fishes associated with estrogenic compounds, implications of this phenomenon, and examples of EDC related research findings by our group in the Potomac River Watershed, USA.
We studied the influence of behavior, water velocity, and physiological development on the downstream movement of subyearling fall‐run Chinook Salmon Oncorhynchus tshawytscha in both free‐flowing and impounded reaches of the Clearwater and Snake rivers as potential mechanisms that might explain life history diversity in this stock. Movement rates and the percentage of radio‐tagged fish that moved faster than the average current velocity were higher in the free‐flowing Clearwater River than in impounded reaches. This supports the notion that water velocity is a primary determinant of downstream movement regardless of a fish's physiological development. In contrast, movement rates slowed and detections became fewer in impounded reaches, where water velocities were much lower. The percentage of fish that moved faster than the average current velocity continued to decline and reached zero in the lowermost reach of Lower Granite Reservoir, suggesting that the behavioral disposition to move downstream was low. These findings contrast with those of a similar, previous study of Snake River subyearlings despite similarity in hydrodynamic conditions between the two studies. Physiological differences between Snake and Clearwater River migrants shed light on this disparity. Subyearlings from the Clearwater River were parr‐like in their development and never showed the increase in gill Na + /K + ‐ATPase activity displayed by smolts from the Snake River. Results from this study provide evidence that behavioral and life history differences between Snake and Clearwater River subyearlings may have a physiological basis that is modified by environmental conditions.
Depletion sampling in combination with multiple-pass electrofishing is an important fisheries management tool for wadeable streams. This combination of techniques has been used routinely by federal and state fishery management agencies for several decades as a reliable means to obtain quantitative data on trout populations or to describe fish community structure. In this paper we review the effects of electrofishing on fish and discuss this within the context of depletion sampling and multiple exposures of fishes to electric fields. The multiple wave forms most commonly used in sampling (alternating current, direct current, and pulsed direct current) are discussed as well as electrofishing induced response, injury and physiological stress. Fish that survive electrofishing injuries are more likely to suffer short and long-term adverse effects to their behavior, health, growth, or reproduction. Of greatest concern are the native, non-target species that may be subjected to multiple electrical shocks during the course of a 3-pass depletion survey. These exposures and their effects on the non-target species warrant further study as do the overall effects of electrofishing on populations and community structure.
In a natural, unaltered river, the location and timing of sturgeon spawning will be dictated by the prevailing environmental conditions to which the sturgeon have adapted. A goal of the Comprehensive Sturgeon Research Program (CSRP; see chap. A) at the U.S. Geological Survey Columbia Environmental Research Center is to identify where, when, and under what conditions shovelnose sturgeon ( Scaphirhynchus platorynchus ) and pallid sturgeon ( S. albus ) spawn in the altered Missouri River so that those conditions necessary for spawning success can be defined. One approach to achieving this goal is to exploit what is known about fish reproductive physiology to develop and apply a suite of diagnostic indicators of readiness to spawn. In 2005 and 2006, gravid shovelnose sturgeon and a limited number of pallid sturgeon were fitted with transmitters and tracked on their spawning migration. A suite of physiological indicators of reproductive state such as reproductive hormones and oocyte development were measured. These same measurements were made on tissues collected from additional fish, presumably migrating to spawn, that were not tagged or tracked. The data presented here indicating the sturgeons’ readiness to spawn are to be evaluated together with their behavior and the environmental conditions. The U.S. Army Corps of Engineers (ACOE) Sturgeon Response to Flow Modification (SRFM; see chap. A) study, initiated in 2006, provides additional opportunities to experimentally evaluate the sturgeon reproductive response indicators relative to changes in flow. In this chapter, we report progress made on identifying and developing the physiological indicators and summarize 2 years’ worth of indicator data collected thus far.
Little is known about the physiological capabilities of young-of-year (YOY) shortnose sturgeon. In this study, plasma osmolality and hematocrit values were measured for YOY shortnose sturgeon following 48-h exposures to 12 different combinations of salinity and temperature. Hematocrit levels varied significantly with temperature and age, and plasma osmolalities varied significantly with salinity and age. Plasma osmolality and hematocrit values were similar to previously published values for other sturgeons of similar age and size in similar treatment conditions. ?? 2010 Springer Science+Business Media B.V.
Juvenile white sturgeon ( Acipenser transmontanus ) were fed three isonitrogenous and isoenergetic diets containing either 35% D-glucose (HC), a mixture of 20% dextrin and 10% cellulose (MC), or 23% cellulose (LC), to investigate the effects of dietary carbohydrate on liver function. After 8-week feeding, body weight gain of fish fed the HC diet was consistently higher than that of fish fed the MC and LC diets, but was not significantly different from the MC-fed fish. Fish fed the HC diet had significantly (p < 0.05) higher feed efficiencies and liver glycogen concentrations than fish fed the MC and LC diets. Sturgeon were injected intravenously with 10 mg kg -1 body weight of sulfobromophthalein (BSP) and post-injection blood taken from the caudal vein at 15, 30, 60, and 120 min. No significant differences in plasma BSP concentrations were found among the treatments at these times. Plasma hemoglobin and activities of aspartate and alanine aminotransferase were not affected by the diets. This study suggests that the HC diet does not adversely affect liver function or weight gain. Inclusion of high dietary levels of digestible and inexpensive carbohydrates in commercial sturgeon feeds seems promising, but long-term feeding trials should be conducted to confirm this assertion.
Total, packed cell and, plasma volume estimates were made for the whole body and selected tissues of rainbow trout by the simultaneous injection of radiolabelled trout erythrocyte ( 51 Cr-RBC) and radioiodinated bovine serum albumin ( 125 I-BSA) tracers. Blood volumes were estimated with both markers separately by the tracer-hematocrit method and as the combination of the 51 Cr-RBC packed cell and 125 I-BSA plasma volumes. Mean whole body blood volume was significantly less when calculated from the 51 Cr-RBC tracer data (3.52±0.78 ml/100 g; ±SD) than when calculated with the 125 I-BSA tracer (5.06±0.86 ml/100 g) or as the sum of the two volumes combined (4.49±0.60 ml/100 g). The whole body hematocrit (28±5%), estimated as the quotient of the 51 Cr-RBC volume divided by the sum of the 125 I-BSA and the 51 Cr-RBC volumes, also was significantly less than the dorsal aortic microhematocrit (36±4%). Estimates of total blood volumes in most tissues were significantly smaller when calculated from the 51 Cr-RBC data than when calculated by the other two methods. Tissue blood volumes were greatest in highly vascularized and well perfused tissues and least in poorly vascularized tissues. The relative degree of vascularization among tissues generally remained the same regardless of whether the red cell or the plasma tracer was used to calculated blood volume. It is not clear whether the expanded plasma volume is the result of the distribution of erythrocyte-poor blood into the secondary circulation or the result of extravascular exchange of plasma proteins.
Studies were conducted to determine whether interactions occur among dietary lysine, arginine and monovalent minerals in rainbow trout. In one experiment, rainbow trout fingerlings were fed diets containing three levels of lysine (2.4, 3.1 and 3.8 g per 100 g diet), two levels of arginine (1.7 and 2.5 g per 100 g diet) and two mixtures of Na + K + and Cl in a 3×2×2 factorial design. The mixtures varied in the proportions of cations to anions such that Cl equalled the sum of Na + and K + (cations − anions = 0 mEq/kg diet) in one mixture and exceeded the sum of Na + and K + (cations − anions = −200 mEq/kg diet) in the second mixture. Growth and efficiency of feed conversion were not affected by dietary lysine and arginine in fish fed diets containing − 200 mEq/kg balance, but when fish were fed diets containing a 0 mEq/kg balance, 3.8% lysine and a combination of 3.1% lysine and 2.5% arginine depressed both measures of response. Trout receiving the 0 mEq/kg cation-anion balance had significantly higher free histidine concentrations and lower free lysine concentrations in muscle and higher hepatic arginase activity (P≤0.01) than those receiving −200 mEq/kg. In another experiment, trout were fed diets containing three levels of K + (21, 191 and 360 mEq/kg), two levels of Na + (21 and 191 mEq/kg) and two levels of Cl − (179 and 347 mEq/kg) in a 3×2×2 factorial design. Growth and efficiency of feed conversion were depressed and hepatosomatic index increased with higher levels of dietary K + (P≤0.01), Na + (P≤0.05) and Cl (P≤0.01), with significant K + x Cl + (P≤0.01) and K + x Na + x Cl (P≤0.05) interactions. Increasing dietary K + resulted in increased levels of muscle free histidine and decreased levels of muscle free lysine and arginine (P≤0.01), while increasing dietary Cl increased muscle free lysine, the effect of which was dependent on dietary potassium (K + x Cl − , P≤0.01). It is concluded that dietary levels of K + , Na + and Cl − , irrespective of overall cation-anion balance of these minerals, affects growth rate, efficiency of feed utilization and the metabolism of basic amino acids in tissues of trout. Excess lysine causes depressed growth and efficiency of feed utilization. These effects were due to a lysine toxicity rather than a lysine-arginine antagonism, as they were not prevented by supplemental dietary arginine.
Walleye (Sander vitreus) is an important sport fish throughout much of North America, and walleye populations support valuable commercial fisheries in certain lakes as well. Using a corrected algorithm for balancing the energy budget, we reevaluated the performance of the Wisconsin bioenergetics model for walleye in the laboratory. Walleyes were fed rainbow smelt (Osmerus mordax) in four laboratory tanks each day during a 126-day experiment. Feeding rates ranged from 1.4 to 1.7 % of walleye body weight per day. Based on a statistical comparison of bioenergetics model predictions of monthly consumption with observed monthly consumption, we concluded that the bioenergetics model estimated food consumption by walleye without any significant bias. Similarly, based on a statistical comparison of bioenergetics model predictions of weight at the end of the monthly test period with observed weight, we concluded that the bioenergetics model predicted walleye growth without any detectable bias. In addition, the bioenergetics model predictions of cumulative consumption over the 126-day experiment differed fromobserved cumulative consumption by less than 10 %. Although additional laboratory and field testing will be needed to fully evaluate model performance, based on our laboratory results, the Wisconsin bioenergetics model for walleye appears to be providing unbiased predictions of food consumption.
Little is known about the effects of brominated flame retardants in teleosts and some of the information currently available is inconsistent. This study examined effects of dietary exposure to 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) on thyroid condition, body mass and size, and gonadal development of zebrafish. Pubertal, 49-day-old (posthatch) fish were fed diets without BDE-47 (control) or with 1, 5 or 25 μg/g BDE-47/diet. Treatments were conducted in triplicate 30-L tanks each containing 50 zebrafish, and 15 fish per treatment (5 per tank) were sampled at days 40, 80 and 120 of exposure. Measurements were taken of body mass, standard length, head depth and head length. Sex (at 40–120 days of exposure), germ cell stage (at 40 days) and thyroid condition (at 120 days; follicular cell height, colloid depletion, angiogenesis) were histologically determined. Whole-body BDE-47 levels at study completion were within the high end of levels reported in environmentally exposed (wild) fishes. Analysis of variance was used to determine differences among treatments at each sampling time. No effects were observed on thyroid condition or germ cell stage in either sex. Reduced head length was observed in females exposed to BDE-47 at 80 days but not at 40 or 120 days. In males, no apparent effects of BDE-47 were observed at 40 and 80 days, but fish exposed to 25 μg/g had lower body mass at 120 days compared to control fish. These observations suggest that BDE-47 at environmentally relevant whole-body concentrations does not affect thyroid condition or pubertal development of zebrafish but does affect growth during the juvenile-to-adult transition, especially in males.
Asian swamp eel, Monopterus albus/javanensis [Zuiew, 1973/Lacepede 1800], has been established in the southeastern USA since at least 1994, yet little is known about its ability to survive low winter temperatures. We use standard thermal methodologies to quantify low temperature responses and provide a detailed description of swamp eel reactions to cold temperatures. When exposed to chronic temperature decreases of 1.0 °C day −1 , swamp eel ceased foraging at 15.0 °C, markedly diminished movements below 11.0 °C, and became incapacitated near 9.6 °C. During critical thermal minima trials, swamp eel exposed to acute temperature drops (0.25 °C min −1 ) tolerated temperatures as low as 6.2 °C. Swamp eel exhibited a moderate cold acclimation response, gaining 0.23 °C in cold tolerance for every 1 °C drop in acclimation temperature. Progressive time-series critical thermal minimum temperatures (CTmin) estimates for eel acclimated to 20.5 °C followed by an acute temperature decrease to 16.0 °C, revealed that cold acclimation may occur in only 8 days. Fringe populations of swamp eel in their native range periodically experience colder winter temperatures, which may explain the ability of introduced populations to survive winter cold fronts in Florida. Understanding Asian swamp eel acute and chronic thermal limits may be useful in assessing dispersal risk and range expansion in the southeastern USA.
The capacity of cortisol, ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I) and 3,3′,5-triiodo-l-thyronine (T 3 ) to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity) were injected with a single dose of hormone suspended in oil and transferred to seawater (SW, 35 ppt salinity) 10 days post-injection. Fish were sampled 24 h after transfer and plasma osmolality and gill Na + , K + -ATPase activity were examined. Transfer from BW to SW induced significantly increased plasma osmolality but not gill Na + , K + -ATPase activity. Cortisol (50 μg g −1 body weight) improved the ability to maintain plasma osmolality and to increase gill Na + , K + -ATPase activity. oGH (5 μg g −1 body weight) also increased hypoosmoregulatory ability and gill Na + , K + -ATPase activity. A cooperation between oGH and cortisol was observed in increasing hypoosmoregulatory ability but not in increasing gill Na + , K + -ATPase activity. rbIGF-I (0.5 μg g −1 body weight) alone was without effect in increasing salinity tolerance or gill Na + , K + -ATPase activity. rbIGF-I and oGH showed a positive interaction in increasing salinity tolerance, but not gill Na + , K + -ATPase activity. Treatment with T 3 (5 μg g −1 body weight) alone did not increase salinity tolerance or gill Na + , K + -ATPase activity, and there was no consistent significant interaction between cortisol and T 3 or between GH and T 3 . The results confirm the classical role of cortisol as a seawater-adapting hormone and indicate an interaction between cortisol and the GH/IGF-I axis during seawater acclimation of Fundulus heteroclitus.