Behavioural salinity preferences of juvenile green sturgeon Acipenser medirostris acclimated to fresh water and full-strength salt water.

To quantify the salinity preference of juvenile green sturgeon Acipenser medirostris, two groups of A. medirostris [140 days post hatch (dph); total length (L(T) ) 38.0-52.5 cm] were acclimated to either near fresh water (mean ± s.e. salinity = 3.2 ± 0.6) or full-strength salt water (34.1 ± 1.2) over 8 weeks. Following acclimation, the two groups were divided into experimental and control groups, where experimental A. medirostris from both freshwater and saltwater acclimations were individually introduced (200-220 dph) into a rectangular salinity-preference flume (maximum salinity gradient: 5-33). Control A. medirostris were presented with only their acclimation water (fresh water or salt water) on both sides of the flume. It was demonstrated that A. medirostris acclimated to both salt water and fresh water spent a significantly greater amount of time on the side of the testing area with the highest salinity concentration (P < 0.05 and P < 0.001, respectively) while control A. medirostris spent an equal amount of time on each side of the flume. These findings indicate that juvenile A. medirostris are not only capable of detecting salt water within the first year of their lives but perhaps are actively seeking out saline environments as they move through a watershed. Establishing A. medirostris salinity preferences provides a better understanding of the early life history of this threatened species, shedding light on possible outmigration timing.

Effects of feeding on thermoregulatory behaviours and gut blood flow in white sturgeon (Acipenser transmontanus) using biotelemetry in combination with standard techniques.

The effects of thermoregulatory behaviours on gut blood flow in white sturgeon Acipenser transmontanus before and after feeding was studied using a blood flow biotelemetry system in combination with a temperature preference chamber. This is the first study to look at cardiovascular responses to feeding in white sturgeon, and also the first time behavioural tests in fish have been combined with recordings of cardiac output, heart rate, cardiac stroke volume and gut blood flow. The results showed strong correlations between gut blood flow and temperature choice after feeding (R(2)=0.88+/-0.03, 6-8 h postprandially and R(2)=0.89+/-0.04, 8-10 h postprandially) but not prior to feeding (R(2)=0.11+/-0.05). Feeding did not affect the actual temperature preference (18.4+/-0.7 degrees C before feeding, 18.1+/-0.7 degrees C, 6-8 h postprandially and 17.5+/-0.5 degrees C, 8-10 h postprandially). Fish instrumented with a blood flow biotelemetry device, and allowed to move freely in the water, had a significantly lower resting heart rate (37.3+/-0.26 beats min(-1)) compared with the control group that was traditionally instrumented with transit-time blood flow probes and kept in a confined area in accordance with the standard procedure (43.2+/-2.1 beats min(-1)). This study shows, for the first time in fish, the correlation between body temperature and gut blood flow during behavioural thermoregulation.

Proteomic and physiological responses of leopard sharks (Triakis semifasciata) to salinity change.

Partially euryhaline elasmobranchs may tolerate physiologically challenging, variable salinity conditions in estuaries as a trade-off to reduce predation risk or to gain access to abundant food resources. To further understand these trade-offs and to evaluate the underlying mechanisms, we examined the responses of juvenile leopard sharks to salinity changes using a suite of measurements at multiple organizational levels: gill and rectal gland proteomes (using 2-D gel electrophoresis and tandem mass spectrometry), tissue biochemistry (Na(+)/K(+)-ATPase, caspase 3/7 and chymotrypsin-like proteasome activities), organismal physiology (hematology, plasma composition, muscle moisture) and individual behavior. Our proteomics results reveal coordinated molecular responses to low salinity - several of which are common to both rectal gland and gill - including changes in amino acid and inositol (i.e. osmolyte) metabolism, energy metabolism and proteins related to transcription, translation and protein degradation. Overall, leopard sharks employ a strategy of maintaining plasma urea, ion concentrations and Na(+)/K(+)-ATPase activities in the short-term, possibly because they rarely spend extended periods in low salinity conditions in the wild, but the sharks osmoconform to the surrounding conditions by 3 weeks. We found no evidence of apoptosis at the time points tested, while both tissues exhibited proteomic changes related to the cytoskeleton, suggesting that leopard sharks remodel existing osmoregulatory epithelial cells and activate physiological acclimatory responses to solve the problems posed by low salinity exposure. The behavioral measurements reveal increased activity in the lowest salinity in the short-term, while activity decreased in the lowest salinity in the long-term. Our data suggest that physiological/behavioral trade-offs are involved in using estuarine habitats, and pathway modeling implicates tumor necrosis factor alpha (TNFalpha) as a key node of the elasmobranch hyposmotic response network.

Fluid dynamics in suspension-feeding blackfish.

Measurements of flow patterns and water velocities inside the oral cavity of blackfish (Orthodon microlepidotus), made with a fiberoptic endoscope and thermistor flow probe, revealed that gill-arch structures act in blackfish as barriers that direct particle-laden water to the mucus-covered roof of the oral cavity, where particles are retained. Gill-arch structures have previously been assumed to be the site of particle retention in suspension-feeding fishes. Water does not pass between these structures in blackfish, and they do not serve as filters that separate particles from the water. These results emphasize the importance of directly assessing flow velocity and direction inside the oral cavity of vertebrate suspension feeders, particularly at the level of the filtering elements.

The cost of chronic stress: impacts of a nonhabituating stress response on metabolic variables and swimming performance in sturgeon.

Metabolic scope for activity (MSA) and critical swimming velocity (U(crit)) were measured in green sturgeon exposed to two stressors daily for 28 consecutive days. The results were compared with unstressed fish in an effort to measure the "cost" of chronic stress. Chronic stress was simulated by exposing fish to a randomized order of acute stressors: a 5-min chasing stressor, a 10-min water depth reduction stressor, or a 5-min confinement stressor. The acute cortisol response to each stressor was initially determined, and the maintenance of that response was verified in 7-d intervals during the chronic stress regime. Exposure to the chronic stress regime resulted in a 25% reduction of MSA caused by significantly increased maintenance metabolic rate (0.27+/-0.01 vs. 0.19+/-0.02 mg O(2) h(-1) g(-1), chronic and control fish, respectively) but did not affect the U(crit) of sturgeon. In addition, a 50% reduction in liver glycogen levels and a twofold increase of resting plasma glucose levels were measured in chronically stressed fish. We conclude that our chronic stress regime resulted in a significant maintenance cost to green sturgeon, possibly because of their inability to habituate to the stressors, but did not decrease their swimming performance.

Comparative environmental tolerances of threatened delta smelt (Hypomesus transpacificus) and introduced wakasagi (H. nipponensis) in an altered California estuary.

In California's Sacramento-San Joaquin estuary, environmental protection and habitat restoration efforts directed at a threatened native osmerid, the delta smelt (Hypomesus transpacificus), are complicated by the presence of a morphologically similar non-native congener, the wakasagi (H. nipponensis), transported to the estuary from upstream reservoirs. In order to better define delta smelt critical habitat and to evaluate the potential for habitat overlap by these two species, we compared the tolerances of the two species to temperature, salinity, and water velocity, environmental factors that vary spatially and temporally within the estuary. For fishes acclimated to 17°C and fresh water (0 ppt), we measured critical thermal maxima and minima, chronic upper salinity tolerance limits, and critical swimming velocities. Wakasagi had higher critical thermal maxima (29.1°C vs. 25.4°C for delta smelt), lower critical thermal minima (2.3°C vs. 7.5°C for delta smelt), higher upper salinity tolerances (26.8 ppt vs. 19.1 ppt for delta smelt), and swam faster (for 6-6.9 cm SL fish, 43.3 cm s-1 vs. 28.2 cm s-1 for delta smelt) than delta smelt. This suggests that the wide seasonal and year-to-year fluctuations in temperature, salinity, and flow typical in the estuary would not exclude wakasagi, although their eggs and larvae may be less tolerant. With respect to these factors, the native delta smelt may be at a physiological disadvantage, particularly in habitats with suboptimal environmental conditions, and may be excluded from shallow-water habitat restoration sites, which are characterized by poor circulation, low flows, and more environmentally extreme conditions. The low abundance of wakasagi in the estuary recorded to date may indicate that factors other than temperature, salinity, and flow determine wakasagi distribution.

Comparative larvivorous performances of mosquitofish, Gambusia affinis, and juvenile Sacramento blackfish, Orthodon microlepidotus, in experimental paddies.

Mosquitofish, Sacramento blackfish, or combinations of both species were stocked in experimental paddies. Cultured Culex tarsalis larvae, stocked weekly into each paddy, and wild Anopheles freeborni larvae were counted by dipping. At the end of the 12 week experiment, paddies were drained and the remaining fish and visible invertebrates counted. Data show the highest number of mosquito larvae in the blackfish-stocked paddies. This low larvivorous ability of blackfish may result from their rapid growth to ca. 70 mm standard length and a consequent shift to a filtering mode of feeding. Although blackfish populations decreased from one-third to one-half of their stocked levels and mosquitofish populations increased to very high levels, mosquito control seemed to be a function of species rather than just the number of predatory fish. The lower number of larvae in the control paddies compared with the blackfish paddies might be attributable to predatory invertebrate communities.

Prey selection by mosquitofish (Gambusia affinis) in California rice fields: effect of vegetation and prey species.

Mosquitofish are widely used for biological control of mosquito larvae in rice fields, but the presence of different types of vegetation or alternative arthropod prey affects the performance of the fish. Feeding experiments were conducted in 4 rice field vegetation zones. Overall, predation was maximal in young and mature rice, moderate in the submerged naiad vegetation, and minimal in areas of open water. A preference for fourth instar Culex tarsalis mosquito larvae over Daphnia pulex and the amphipod Hyalella azteca was demonstrated. Second nymphal stage corixid bugs, Cenocorixa sp., were avoided; a similar notonectid, Buenoa sp., was eaten in amounts comparable to the D. pulex and H. azteca. No preference between Culex tarsalis and Anopheles freeborni mosquito larvae was detected.

Mosquito control in wastewater: a controlled and quantitative comparison of pupfish (Cyprinodon nevadensis amargosae), mosquitofish (Gambusia affinis) and guppies (Poecilia reticulata) in Sago pondweed marshes.

We compared the abilities of pupfish, mosquitofish and guppies to control mosquitoes in wastewater marshes. All species of fish reduced mosquito emergence. When fish population densities were similar, fish reduced emergence to similar levels. As experiments progressed, guppies developed greater population densities and provided better mosquito control than mosquitofish, which developed greater densities and better control than pupfish. Fish also reduced numbers of zooplankton, and guppies increased total plant biomass, suggesting fish may influence the ability of wastewater marshes to treat wastewater.

Using specific antisera to neutralize ACTH in sturgeon: a method for manipulating the interrenal response during stress.

Interrenal function and the magnitude of the stress response were assessed in green sturgeon (Acipenser medirostris) passively immunized with antisera directed against adrenocorticotropic hormone (ACTH). The nucleotide sequence encoding ACTH was determined using reverse transcriptase polymerase chain reaction (RT-PCR). We identified two isoforms of ACTH that differ at a single site (position 26) in the 39 AA peptide. Both forms of green sturgeon ACTH (gsACTH1-39) display 100% homology with both sequences of white sturgeon ACTH (wsACTH1-39). The N-terminal portion of gsACTH also shares absolute identity with the comparable portion of human ACTH (hACTH). However, we identified considerable sequence divergence in the C-terminal domain between gsACTH and hACTH. Species-specific anti-ACTH sera were generated by vaccinating sheep against the C-terminal portion of gsACTH (gsACTH26-39). The peptide was covalently linked to a carrier protein (keyhole-limpet-hemocyanin [KLH]) to further enhance its immunogenicity. The anti-gsACTH sera recognized gsACTH1-39 and the immunogenic peptide (gsACTH26-39), but did not interact with hACTH1-39. To assess the impact of the antisera, fish were passively immunized with anti-gsACTH26-39 sera or anti-KLH sera and challenged with a hACTH1-39 injection on day 1 followed by a 1-min air emersion stressor on day 2. The magnitude and duration of the secretory response induced by hACTH did not differ (P > .05) between groups. Conversely, the magnitude of cortisol secretion induced by air emersion was significantly attenuated (P < .05) in fish passively immunized against gsACTH26-39. Collectively, these data demonstrate that the targeted antisera used in this study can discriminate between mammalian and green sturgeon ACTH and moderate the in vivo response to a stressor.

Juvenile coho salmon locomotion and mosaic muscle are modified by 3',3',5'-tri-iodo-L-thyronine (T3).

Studies of maximum aerobic swimming performance in smolting juvenile salmonids indicate that these animals may be aerobically compromised during downstream migration. To test our hypothesis that hyperthyroid status contributes to decreased swimming performance through modification of muscle contractility in juvenile (112 mm mean total length) coho salmon (Oncorhynchus kisutch), we measured swimming performance and isolated muscle bundle contractility of fish implanted with 3',3',5'-tri-iodo-l-thyronine (T3) pellets, of fish implanted with sham pellets and of fish with no pellet implantation (control group). After 3 weeks (N=12-13), critical swimming speeds (maximum aerobic swimming speed or U(crit)) were measured. Muscle bundles (N=15-16) were dissected from the hypaxial musculature and stimulated to measure the force and velocity of an isometric twitch and tetani. T3-treated fish demonstrated visible morphological changes associated with smoltification. Mean values of U(crit) were significantly decreased and the prolonged contraction (tetani) and twitch rates of contraction, relaxation and maximum force were significantly increased by T3 treatment compared with both the sham and control fish. Hematocrit, body mass and body length were not significantly affected by T3 treatment. In conclusion, we suggest that the reported decrease in U(crit) during salmonid smoltification may be mediated by endogenous T3-induced contractile modification of mosaic muscle fibers.

Time of day and water temperature modify the physiological stress response in green sturgeon, Acipenser medirostris.

The effects of time of day and water temperature on the acute physiological stress response were investigated in young-of-the-year green sturgeon (Acipenser medirostris). The response to a 1-min air-emersion stressor was assessed during the day (08.00 h) and at night (20.00 h), as well as after acclimation to either 11 degrees C or 19 degrees C. Blood samples were collected prior to stress and at several times after exposure to the stressor, and plasma concentrations of cortisol, lactate, and glucose were determined. The magnitudes of cortisol (19.1 ng ml(-1) vs. 4.9 ng ml(-1)) and lactate (190.6 mg l(-1) vs. 166.7 mg l(-1)) were significantly higher in fish stressed at night when compared with the day. There were no significant differences in glucose levels between time periods. Although, acclimation temperature did not affect peak cortisol concentrations (56.7 and 50.3 ng ml(-1) at 11 degrees C and 19 degrees C, respectively), the duration of the response was significantly extended at 11 degrees C. Post-stressor lactate increases were similar between temperature groups, but at 11 degrees C post-stressor glucose levels were significantly increased through 6 h, suggesting stressor-induced glycogenolysis and gluconeogenesis or decreased glucose utilization. These data demonstrate that the physiological stress response in green sturgeon is modified by both time of day and temperature.

Cardiorespiratory responses of white sturgeon to environmental hypercapnia.

Cardioventilatory variables and blood-gas, acid-base status were measured in cannulated white sturgeon (Acipenser transmontanus) maintained at 19 degrees C during normocapnic and hypercapnic (Pw(CO(2)) approximately 20 Torr) water conditions and after the injection of adrenergic analogs. Hypercapnia produced significant increases in arterial PCO(2), ventilatory frequency, and plasma concentration of cortisol and epinephrine, and it produced significant decreases in arterial pH and plasma concentration of glucose but no change in arterial PO(2), hematocrit, and concentration of lactate or norepinephrine. Hypercapnia significantly increased cardiac output (Q) by 22%, mean arterial pressure (MAP) by 8%, and heart rate (HR) by 8%. However, gut blood flow (GBF) remained constant. In normocapnic fish, phenylephrine significantly constricted the splanchnic circulation, whereas isoproterenol significantly increased Q and produced a systemic vasodilation. During hypercapnia, propranolol significantly decreased Q, GBF, MAP, and HR, whereas phentolamine significantly decreased MAP and increased GBF. These changes suggest that cardiovascular function in the white sturgeon is sensitive to both alpha- and beta-adrenergic modulation. We found microspheres to be unreliable in predicting GBF on the basis of our comparisons with simultaneous direct measurements of GBF. Overall, our results demonstrate that environmental hypercapnia (e.g., as is experienced in high-intensity culture situations) elicits stress responses in white sturgeon that significantly elevate steady-state cardiovascular and ventilatory activity levels.

Sublethal effects of three pesticides on Japanese medaka.

One- to 2-day-old medaka (Oryzias latipes) larvae were exposed for 4 days to the rice field pesticides methyl parathion, molinate, carbofuran and a mixture of all three. Pesticide concentrations were one-half the 96 h LC50 ("high concentration") and levels approximating those measured in receiving waters from rice field runoff ("low concentration"). Maximum swimming speed, spontaneous muscular activity, acetylcholinesterase activity, dry weight, RNA:DNA ratio, and five morphometric variables were determined at the end of the exposures. Larvae were retained for an additional 10 days in non-contaminated water, and the same measurements taken to investigate residual effects. Results are compared to a parallel study on striped bass larvae to evaluate the suitability of this species as a surrogate for the bass in toxicological studies involving sublethal exposures. There was no relationship between mortality rate and pesticide exposure either during the exposures or during the ten day subsequent period. Only the high concentration of carbofuran caused an impairment of swimming performance. Spontaneous activity was stimulated in the high concentration of molinate and the combined pesticides groups. Acetylcholinesterase was severely inhibited in parathion and molinate, and this persisted in some cases after 10 days in non-contaminated water. The pesticides had little effect on growth rate except for molinate which acted as a stimulant. Combining the three pesticides caused a less than additive effect. Except for decreases in acetylcholinesterase, the sublethal effects of the pesticides tested at the very low concentrations used were subtle. Apparently, larvae of this species are less sensitive to these pesticides than are striped bass larvae.

Red cell function of carp (Cyprinus carpio) in acute hypoxia.

The red cell function of carp, subjected to acute hypoxia, was studied. During hypoxic exposure red cell water content, sodium and chloride concentration and pH increased, whereas plasma sodium and chloride concentrations decreased. Treatment of the animals with a beta-adrenergic antagonist, propranolol, before the onset of hypoxia, largely inhibited the increase in red cell water content, diminished the changes in red cell pH and prevented the changes in red cell and plasma sodium concentration. The red cell chloride concentration increased also in propranolol-treated animals thus illustrating the effect of the deoxygenation of haemoglobin on the ion concentrations of red cells. These data indicate that adrenergic activation of sodium/proton exchange across red cell membrane plays a role in the acute responses of carp to hypoxia.

Physiological responses of fathead minnow larvae to rice pesticides.

Newly hatched fathead minnow (Pimephales promelas) larvae were exposed for 4 days to two pesticides and ambient receiving waters to simulate conditions in the Sacramento River, California, during the striped bass spawning season which coincides with pesticide use in adjacent rice culture. Carbofuran and molinate were tested at two concentrations: a higher level approximating one-half the LC50 and a level much lower that is similar to that seen in the receiving waters of Colusa Basin Drain. Physiological measurements were made immediately after the exposures and again after a 10-day recovery period in noncontaminated waters. These included growth rate, swimming capacity, response to a mild electric shock, upper and lower lethal temperatures, and activity of acetylcholinesterase in whole-body homogenates. The higher concentrations of carbofuran and molinate caused reductions in swimming capacity, an increased sensitivity to the electric shock, and a reduction in upper lethal temperature. Acetylcholinesterase was reduced in those larvae exposed to the higher levels of carbofuran. In general, the lower levels of pesticide exposure caused no measureable effects nor did exposure to water from Colusa Basin Drain.

Gut blood flow in fish during exercise and severe hypercapnia.

This paper reviews the effects of exercise and hypercapnia on blood flow to the splanchnic circulation. Brief struggling behaviours are known to decrease blood flow to the gut (GBF). Likewise, prolonged swimming in unfed fish has been shown to reduce GBF in proportion to the increased oxygen uptake. Therefore, the normal postprandial increase in GBF theoretically should be impaired whenever fish are active. However, indirect evidence suggests that GBF is spared to some degree when fed fish swim continuously but at a cost (10-15%) to their critical swimming speed. Severe respiratory acidosis can be created by the new intensive aquaculture settings that use oxygen injection into re-circulated water. The only study so far to examine the effects of severe hypercapnia on GBF and its regulation showed that routine GBF and alpha-adrenergic control of GBF remained normal in unfed white sturgeon (Acipenser transmontanus). However, severe hypercapnia produced a hyperactive state and increased sensitivity of GBF to struggling. As a result, routine GBF was maintained for a short period of time. Thus, environmental changes such as severe hypercapnia can indirectly impact GBF through altered struggling behaviour, but the implications of the overall reduction in GBF to food assimilation have yet to be established.