摘要:

A maternally transmitted, noninfectious disease known as the Cayuga syndrome caused 100% mortality in larval offspring of wild-caught landlocked Atlantic salmonSalmo salarfrom several of New York's Finger Lakes. Survival of lake troutSalvelinus namaycushfrom Lakes Erie and Ontario was also impaired, but not until yolk absorption was nearly complete; moreover, mortality was greatly reduced relative to that of the salmon (range: 5–87%). Tissue concentrations of thiamine hydrochloride were severely reduced in these salmonid fish relative to unaffected control stocks. Afflicted Atlantic salmon treated with thiamine by yolk-sac injection or by bath immersion recovered completely from the Cayuga syndrome, as evidenced by the quantified reversal of abnormal swimming behaviors only 2 d after treatment and by the excellent survival (>95%) of the treated Atlantic salmon through 1.5 months of feeding. These data represent the first evidence of a vitamin deficiency causing the complete reproductive failure of an animal population in nature. These lethal vitamin deficiencies are presumably caused by a diet of alewivesAlosa pseudoharengus, nonnative forage fishes of the herring family that exhibit high thiaminase activity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0167:NOTDCR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We tracked 10 ultrasonically tagged shortnose sturgeonsAcipenser brevirostrurnduring spring in the Merrimack River to investigate spawning. Seven fish in 1989 and six fish in 1990 were tracked intensively to identify the timing and location of spawning and to characterize spawning habitat. In mid-April 1989 and 1990, fish moved upstream to just below head of tide, concentrating in a 2-km reach at river kilometers 30–32 (measured from the mouth) at Haverhill, Massachusetts. The estimated spawning time was a 5-d period (26–30 April) in 1989 and an 8-d period (22–29 April) in 1990. Spawning sites covered about 10.5 ha in 1989 and 13.5 ha in 1990. Fish spawned as river temperature increased from 9.6 to 14.0°C and river discharge decreased from 390 to 240 m3/s. Physical characteristics of spawning sites were boulder–rubble substrate, water depth of 1.8–5.5 m, and bottom water velocity of 0.3–0.7 m/s. We captured no ovulating females but verified successful spawning in 1990 by capturing two live embryos. Gill-net captures and telemetry during spring showed that some males moved to the spawning area annually. The low abundance estimates of spawning fish (9 in 1989 and 16 in 1990) indicate that the shortnose sturgeon population in the Merrimack River is the smallest yet identified and is likely vulnerable to extirpation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0179:SOTSSI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We investigated the ultrastructure of spermatozoa and some physiological and biochemical parameters of semen in muskellungeEsox masquinongy. Ultrastructure of spermatozoa analyzed with scanning and transmission electron microscopes revealed a spherical head, 1.5 um in diameter. Unlike the spermatozoa of other teleost fishes, an elongated midpiece with abundant mitochondria was found to be characteristic for muskellunge spermatozoa. Three techniques for measuring sperm concentration, counting with a hemacytometer, spermatocrit, and spectrophotometric methods, provided similar results (19.7 ± 6.1 × 109sperm/mL). The spectrophotometric method is recommended because it is rapid and requires only small amounts of semen. Ionic concentrations and osmolality (289 ± 16.8 milliosmols/kg) of seminal plasma were reported. Sodium (129 ± 6.7 mM) and potassium (27.88 ± 3.27 mM) concentrations were closer to levels found in the seminal plasma of salmonids than cyprinids. Aspartate aminotransferase (AspAT) activity was measured with and without supplement of pyridoxal phosphate (PLP) from sperm extracts. A 96% increase of AspAT was found when PLP was included in the assay. We confirmed the presence of antiproteinase activity (against cod trypsin) in seminal plasma of muskellunge. Using the flow cytometry method, we estimated that the DNA stainability of muskellunge spermatozoa was 0.188 ± 0.008 times that of red blood cells (TRBC) from diploid rainbow troutOncorhynchus mykiss. The DNA stainability of muskellunge spermatozoa was significantly lower than that of muskellunge embryonic cells, which was 0.474 times that of the TRBC (2.21 pg DNA/cell, based on the internal standard of TRBC of 4.66 pg DNA/cell).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0187:COMSIU>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We investigated the effects of potassium, sodium, glucose, and calcium concentrations, alone or in combinations, on sperm motility in muskellungeEsox masquinongy. Sperm motility was evaluated by the duration of sperm movement and the initial percentage of motile sperm. The osmolality of diluents rather than the specific ions or nonelectrolyte played a major role in the regulation of sperm motility in muskellunge. Sperm were fully activated (>80%) when the concentration was lower than 50 mM of KCl and NaCl, or 100 mM glucose (all in 30 mM tris–HCl at pH 8.0). A small percent of spermatozoa could be activated at 150 mM KCl and NaCl, or 300 mM glucose, which were hypertonic to the seminal plasma. The duration of sperm movement was up to 6–7 min at 12°C in a solution of 100 mM glucose or 50 mM NaCl. Spermatozoa had a prolonged duration of movement in potassium solutions, up to 120 min at 12°C in a solution of 100 mM KCl. The prolonged duration of movement might be caused by reactivation of sperm or gradual activation of sperm motility. Calcium had an inhibitory effect on sperm motility in muskellunge, starting at 3 mM CaCl2with 30 mM tris–HCl at pH 8.0. Semen diluted in calcium-supplemented solutions did not disperse well, and the sperm tended to form clumps. The mechanism involved in muskellunge sperm motility control markedly differs from that in salmonids (inhibitory function of K+and activatory role of Ca2+) and cyprinids (no effect of Ca2+).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0195:COMSIE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The objectives of this study were to evaluate seasonal changes in the energy density of age-0 and age-1 muskellungeEsox masquinongyand to compare energy density to various estimates of condition. Three treatment groups of muskellunge were evaluated to determine temporal changes in energy density (J/g wet weight [ww]), water content, condition factor (KTL;K=W/L3, whereW= weight andL= total length in centimeters), and relative weight (Wr.; ratio of actual to “standard” weight) through the first year following hatching. Treatment groups were (1) hatchery (muskellunge reared and maintained in hatchery ponds), (2) stocked (hatchery-reared muskellunge stocked in lakes), and (3) natural (muskellunge naturally produced in lakes). Energy levels and relative condition were compared for fish 4 and 11 months old. Differences in energy density were observed between all three treatment groups. An average overwinter reduction of 494 ± 192 J/g ww in energy density was observed over all treatment groups combined. Natural fish lost less energy (8%) over winter than either hatchery (12%) or stocked fish (15%). A simple linear model effectively relates energy to indices of condition for muskellunge. A weak positive relation (P< 0.0001,r2= 0.39, 0.40, and 0.43) was observed between dry weight energy density and three indicators of fish condition (percent water,K, andWr). Our results show that condition indices may not be the best indicators of seasonal fluctuations in total energy within and between fish populations. Seasonal fluctuations in energetic values for a population can be more accurately determined through assessment of percent water in individual fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0203:AOSCIE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We estimated the maintenance food requirements and examined the response to shortterm (38–64-h) food deprivation of larval walleyeStizostedion vitreumin the laboratory. First-feeding larvae (10.0–10.7 mm total length; 0.74–0.82 mg mean dry weight) required maintenance rations,Rmaint, of 7–11%·d−1when feeding on cyclopoid copepods at 15–22°C. Estimates ofRmaintincreased with water temperature. Based on theseRmaintestimates and functional response models from a previous study, we estimated that the prey (cyclopoid copepod) abundances,pmaint, necessary to allow walleye larvae to attainRmaintwould decline from 10 to 27 prey·L−1for larvae of less than 1 mg dry weight (<10.9 mm) to less than 2 prey·L−1for larvae of 1.5 mg or more dry weight (> 11 .9 mm). The effects of food deprivation varied with walleye body size and water temperature. The highest rates of mortality and weight loss were observed in larvae of 1.5–3.5 mg dry weight (11.9–14.6 mm), and the rate of weight loss increased significantly with increasing temperature. Energy densities (J·mg−1) of walleye larvae declined with body size but were not significantly affected by food deprivation or water temperature. Mortality rates were positively related to rates of weight loss during food deprivation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0211:MFRART>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The endemic, haplochromine, cichlid species flock of Lake Malaŵi represents the most diverse assemblage of fishes of any of the world's freshwater lakes. Of particular interest are the interspecific relationships that permit so many species to coexist in this unique ecosystem. We hypothesized that a detailed study of the feeding associations among three sand-dwelling species,Taeniolethrinops praeorbitalis,Cyrtocara moori, andProtomelas annectens, would provide the necessary information needed to determine if these species are effective in harvesting specific food resources.Taeniolethrinops praeorbitalisfeeds by plunging its snout into the sand, engulfing a mouthful of sand, retaining prey items, and expelling the sand through its gills. Immediately afterT. praeorbitalisplunges into the sand, other species, includingC. mooriandP. annectens, move closer and begin to forage on the invertebrates suspended in the water column by the disturbance of the substrate or expelled through the gills ofT. praeorbitalis. The gap between the gill rakers ofT. praeorbitalisis significantly (P< 0.05) wider than that of the other two species; the interraker gaps ofC. mooriandP. annectensare not significantly (P> 0.05) different from each other. MostP. annectensconsumed small Arthropoda and Cladocera (0.3–0.8 mm), whereas mostC. mooriandT. praeorbitalisconsumed chironomids (mean prey size = 4.2 mm). Although there was an association with interraker gap size and prey size whenP. annectensandT. praeorbitaliswere compared, this relationship was not present when the stomach contents and interraker gap ofC. mooriwas contrasted with those of the other two species. Thus, we concluded that differences in prey size among these three species is a function of interraker gap, prey selectivity, and foraging behavior.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0224:CFROTL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We collected gut contents from northern squawfishPtychocheilus oregonensiscaptured in the Clearwater River, Idaho, 0–6 km from its confluence with the Snake River, following the release of 1.1 million yearling chinook salmonOncorhynchus tshawytschafrom the Dworshak National Fish Hatchery. Before the hatchery release, northern squawfish gut contents (by weight) in the study area were 38% crayfishPacifastacusspp., 26% insects, 19% nonsalmonid fish, and 16% wheat kernelsTriticumspp. Juvenile salmonids constituted 54% of gut contents about 24 h after the hatchery release, 78% after 5 d, and 86% after 7 d. The mean number of salmonids per gut (1.2) after release was higher than typically seen in guts from northern squawfish collected in mid-reservoir areas away from hydroelectric dams on the Snake and Columbia rivers. Length-frequency distributions of juvenile salmonids eaten and those captured in a scoop trap 4 km upstream of the study area indicated that northern squawfish were selectively feeding on the smaller individuals. We attribute the high rates of predation in the study area to the artificially high density of juvenile salmonids resulting from the hatchery release and to the physical characteristics of the study area in which the river changed from free flowing to impounded. Our results suggest that northern squawfish can quickly exploit hatchery releases of juvenile salmonids away from release sites in the Columbia River basin.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0230:FRBNST>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Weight change in age-0 coho salmonOncorhynchus kisutchat about natural density was negatively related to the density of juvenile steelhead (anadromous rainbow troutO. mykiss) in a 6-week experiment conducted in July–August 1993 in the north and south forks of Caspar Creek, California. The experiment used 12 enclosed stream sections, each containing a pool and a portion of upstream riffle, with two replicates of three steelhead densities—zero, natural density (1×), and twice the natural density (2×)—on both the north and south forks. The natural density of coho salmon was about one-sixth the density of steelhead. Coho salmon survival was high (87% overall) and not related to treatments. In the north fork, coho salmon weight change was positive in zero density steelhead treatments, zero in 1× treatments, and negative in 2× treatments. Coho salmon weight change in the south fork was less favorable than in the north fork but was also negatively related to the density of steelhead. These results indicate that under some conditions resource partitioning by salmonid species does not eliminate negative interspecific interactions.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0237:EOSDOG>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We investigated habitat use of wild brown troutSalmo truttain Gilchrist Creek, Michigan, with and without a parallel cohort of introduced steelheadOncorhynchus mykiss. This stream is typical of the region, having a low-gradient, stable discharge and a high sand bedload. By snorkeling, we evaluated seasonal habitat use in two stream reaches before and after steelhead introduction to one of the reaches. Age-0 brown trout occupied stream margins soon after emergence, using cover provided by aquatic vegetation growing on sand and silt substrates. By summer and fall, brown trout moved into deeper water and used more diverse cover types. From summer to fall, the smaller age-0 steelhead used lower current velocities than did age-0 brown trout. Similar water depth, substrate, and cover were used by the two species. At the densities studied, age-0 brown trout habitat use did not change in response to the presence of age-0 steelhead. We believe that three factors minimized the effect of steelhead: (1) the larger size of the brown trout, which gave them a competitive advantage; (2) vertical habitat segregation with steelhead suspended in the water column and brown trout near or at the bottom; and (3) temporal differences in habitat ontogeny with shifts of older, larger fish to deeper, faster water. These factors may permit these two species to coexist in low-gradient rivers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0244:EOJSOJ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor