摘要:

We used protein electrophoresis to study the distribution of hybrids between Pecos pupfishCyprinodon pecosensisand introduced sheepshead minnowC. variegatusin the Pecos River, New Mexico–Texas. Pecos pupfish populations in New Mexico apparently are free of hybrid influence except in waters near the New Mexico–Texas state boundary. In Texas, hybrids have replaced Pecos pupfish throughout 430 km of the Pecos River and have spread into downstream areas well outside the recorded range of Pecos pupfish. Hybrids are nearly ubiquitous in waters peripheral to the river, occurring in irrigation canals, reservoirs, and water-filled, commercial gravel pits. Unintrogressed Texas populations of Pecos pupfish occur only in a small tributary of the Pecos River and in a large gravel pit. Similarities in the genetic structure of hybrid pupfish populations in the Pecos River and peripheral waters suggest that the spread of alleles characteristic of sheepshead minnow has been accomplished by dispersal of hybrids, rather than by multiple introductions of sheepshead minnow.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0277:GSOPPP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Habitat use, feeding behavior, and growth of native brook troutSalvelinus fontinalisand hatchery brown troutSalmo truttawere compared in an experiment in which the two species were held alone and together in laboratory stream channels at 14°C. Microhabitat location and vertical distribution of brook trout within the stream channels shifted in the presence of brown trout, and the frequency with which brook trout initiated aggressive interactions declined. Prey capture rates were higher for brown trout than for brook trout in single- and mixed-species trials, and higher for both species when they occurred alone than when they were together. Brook trout and brown trout in single-species trials maintained weight, but did not grow. In the presence of brown trout, however, brook trout lost weight. Instantaneous growth rates of brown trout in mixed species trials were positive. In the presence of brown trout, 33% of the brook trout contracted the fungusSaprolegniasp. and died; brown trout were never infected nor were brook trout in single-species trials. If these changes in behaviors and growth rates extend to natural settings in which brook trout and brown trout co-occur, they may contribute to an explanation for the observed decline of brook trout abundance in eastern North America.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0287:IBNBTA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Direct underwater observation was used to quantify numbers and locations of eight species of fish in 100-m sections along a 1,200-m reach of Sagehen Creek, California, at biweekly intervals between 5 July and 22 September 1983. Most of the eight species exhibited significant short-term changes in abundance and reached peak abundance at different times. Total fish abundance was highest in mid-July; the Margalefindex ofdiversity was highest in mid-August. Lahontan redsideRichardsonius egregius, Tahoe suckerCatostomus tahoensis, and mountain suckerC. platyrhynchusappeared to migrate from a downstream reservoir into the stream during the spawning season. In addition, fish were not distributed evenly in the study reach. All species tended to prefer pool habitat and pools were not uniformly distributed. Relative fish composition determined at long-term permanent sections by electrofishing was not significantly associated with most underwater counts made at different times or stations. This study illustrates mobility of an entire fish assemblage and indicates how long-term studies of fish populations may be greatly influenced by the timing and placement of samples.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0297:SSCICA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The composition of fatty acids in the tissue of hearts of striped bassMorone saxatiliswas determined by a chemometric method, consisting of methanolysis of the tissue, gas chromatography of the resulting fatty acid methyl esters, and multivariate statistical treatment of the analytical data. Striped bass from spawning stocks in the Hudson River, the Roanoke River, and the Chesapeake Bay area had significantly different profiles of 13 selected fatty acids, although the spread among individuals within stocks was considerable, In a training set of 49 striped bass, all were correctly classified; in a test set of 19 samples, 84% were assigned to the correct stock.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0307:DOSBSA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Mated pairs of convict cichlidsCichlasoma nigrofasciatumwere exposed to one of two acidities (pH 5.0–5.5 and pH 7.0) and allowed to breed. Two conspecifics similar in size to the parents were placed in the tank to act as objects of parental aggression. These conspecifics were isolated from the parents by a grid barrier that allowed free visual and chemical interchange between conspecifics and parents. Significant alterations in brooding behaviors and aggressive activities occurred in pairs exposed to pH 5.0–5.5 compared to those at pH 7.0. Females reduced brooding behaviors at lower pH and males increased brooding behaviors to compensate for reductions by females. Aggressive behaviors, especially by males, increased under low-pH stress. Increased visual aggression may reduce the need for physical altercation in stressed environments.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0315:EOACSO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Parr of Atlantic salmonSalmo salarwere exposed to two sublethal flow-through concentrations (averaging 0.2 and 1.0 mg/L) of Hibernia oil-water mixture for up to 40 d to determine relative importance of loss of feeding and food conversion for this juvenile life stage. Oiled parr showed reduced growth for 14 d before growth rates approached those of controls. There were also more weight-losing parr in oiled groups than in control groups. Reduction in growth coincided with reduced food conversion efficiency rather than reduced food intake. Food conversion efficiency was lowest for parr experiencing the higher oil exposure. Net efficiencies in both oiled groups returned to control levels within 2 to 3 weeks, although overall efficiencies in oiled groups lagged behind the control group. Liver glycogen levels were generally lower in oil-exposed parr, whereas liver protein content and the liver-somatic index were higher in parr exposed to the highest concentration of oil. Energy reserves were lower in pan that lost weight during the experiment in comparison with weight-gaining pan. Results suggest that medium-term (2 weeks to 1 month) exposure to low concentrations of oil may have transitory effects on Atlantic salmon parr, but that chronic oiling may impair growth and may influence the timing of length-dependent smoltification.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0322:GAFCBA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We examined cell surface molecules on spermatozoa of rainbow troutOncorhynchus mykissand their requirement during fertilization. A library of monoclonal antibodies was produced against surface antigens of rainbow trout sperm. Three types of antibodies were identified: most of the antibodies cross-reacted with two or more of the somatic cells tested; two cross-reacted only with brain tissue; and two – FS43 and FS 101 – were specific for sperm. All cross-reacted with sperm from chum salmonO. keta, coho salmonO. kisutch, and chinook salmonO. tshawytscha. The amount of sperm-specific antibody required to saturate the antigenic sites was significantly different for sperm from different males and was not related to total cell number. Fertility was reduced in a dose-dependent manner only for sperm preincubated with varying concentrations of antibody FS 101. Using indirect immunofluorescence, we observed that the two antibodies specific for spermatozoa restricted their binding to the head region of the sperm and were similar in their distributional patterns. These results support the hypothesis that a specific site present on the surface of rainbow trout spermatozoa participates in interactions necessary for fertilization.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0333:SSARFF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The reasons for consistent failure of razorback suckerXyrauchen texanusyear-classes in Lake Mohave, Arizona–Nevada, are not entirely understood. To date, egg and larval predation by nonnative fishes is considered the most likely explanation, but food limitation may influence larval mortality. Our experiments in rearing razorback sucker larvae in ponds fertilized at three levels (“high,” “medium,” and “low”) with mean invertebrate densities of 43.3, 23.7, and 12.5 organisms/L, respectively, did not result in significant differences in larval survival (77.0, 89.8, and 67.4%, respectively). However, total larval growth was greater at the two higher invertebrate densities. Biovolume of food but not numbers of food organisms in guts increased linearly with growth of larvae. Numbers and biovolumes of food items did not differ relative to fertilization treatment. First foods of larval razorback suckers were diatoms, detritus, and algae, Soon thereafter, small rotifers and chironomids were taken, and larger organisms, primarily cladocerans, were selected by larger larvae. Year-class failure of razorback sucker in Lake Mohave may be attributable to nutritional deficiency at the lowest recorded densities of reservoir zooplankton. However, starvation or food-related problems do not seem likely at the higher Lake Mohave zooplankton densities, which are at least as great as the invertebrate densities in our low-fertilization treatment ponds.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0340:EOFAOS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The number and size of larval fish samples are usually determined arbitrarily, despite the influence of these decisions on the precision of abundance estimates and the ability to detect differences among population estimates. Review of the literature suggests that most surveys of larval fish are based on few (median, 4), large (median, 300 m3) samples. To evaluate current sampling designs, we developed a model, based on published data, to predict the variance in larval fish abundance among replicate samples. Inter-replicate variance (s2) is strongly related to mean abundance (x) as: log10s2= 0.19 + 1.74·log10x;r2= 0.93,P< 0.0001. This relationship was tested with an extensive data set collected in the Hudson River, New York (weekly samples over 14 years in 12 regions of the 250-km-long river), and was found to be general across environments, life history stages, and species. The model was not affected by sample volume, Our analysis shows that half of published studies estimated larval abundance with a coefficient of variation of the mean (SE/x) of 0.5 or more and could only detect order-of-magnitude differences among sites or time periods. Thes2/xequation provides guidelines to select the number and size of samples that should be taken to achieve a required level of precision and to detect a given difference among population means.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0356:SLFPCO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Nonpoint-source pollutants are implicated in the global acidification of fresh waters. Our ability to differentiate the effects of point-source and nonpoint-source pollution on the acidification of large rivers is limited. Most studies of point-source discharges have been concerned with municipal programs for reducing biochemical oxygen demand, bacterial counts, and total phosphorus; few have addressed acidification of rivers. Because of the meager information on the role of nonpoint-source and industrial pollution in the acidification of large rivers, we examined long-term trends (and cyclic seasonal events) in pH, alkalinity, and selected ions in the lower Mississippi River basin from 1958 to 1986. Time-series analyses disclosed significant declines in pH and alkalinity and increases in strong acid anions in the lower 300 km (industrial corridor) of the lower Mississippi River. However, upstream from most industry on the Mississippi River and throughout the Atchafalaya River, where agricultural development has predominated, long-term trends in those characteristics were variable or nonsignificant.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0369:AOTLMR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor