摘要:

We estimated actual 2-week mortalities of postlarval and juvenile brown shrimp in a Galveston Bay salt marsh by comparing densities of cohorts throughout the spring. Mortalities ranged between 33% and 61% in 1982 and 23% and 39% in 1987. Brown shrimp mortality in predator-exclusion cages during 1987 was less than 3%. These data and published information on food requirements, diseases, and physical tolerances suggest that predation is usually the major direct cause of brown shrimp mortality in estuarine nurseries of the northern Gulf of Mexico. Southern flounderParalichthvs lethostiginawas the dominant fish predator on brown shrimp during the spring, and appeared to be responsible for a large portion of brown shrimp mortality. In laboratory experiments, the presence of smooth corcigrassSpartina alterniflorareduced predation rates of southern flounder and some of the other fish predators examined. Predation rates in general increased in proportion to increased prey densities. Thus, low water levels in the marsh, which reduce access by brown shrimp to intertidal vegetation and increase their densities on nonvegetated bottom, probably result in increased brown shrimp mortality. Mortality and growth may also interact, and predation pressure should be reduced as brown shrimp grow and exceed optimal prey size. Indeed, mortality in the marsh appeared to decline as brown shrimp size increased.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0693:MOYBSP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We determined the concentrations of RNA and DNA in white muscle of rainbow troutOncorhynchus mykissand fathead minnowPimephales promelasthat had been frozen in either liquid nitrogen, a lowtemperature freezer (–80°C), or a household freezer (–20°C), or had been left 1–24 h after death in either wet ice or cold water (8.5–9.5°C). Both RNA and DNA were resistant to enzymatic breakdown because their concentrations and the RNA:DNA ratio did not differ significantly among treatments in either species. However, there was a tendency for muscle DNA concentration to decrease in fathead minnow stored in water for 24 h. Paired samples of rainbow trout muscle, both of which were frozen in liquid nitrogen but one of which was thawed and refrozen before analysis, differed significantly in DNA concentration and RNA:DNA ratio. The refrozen samples had significantly lower DNA concentrations, which led to significantly higher RNA: DNA ratios.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0709:NEOTCA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We estimated the nuclear DNA content of unfixed erythrocytes of the grass carpCtenopharyngodon idellaby fluorescence flow cytometry using propidium iodide as a fluorochrome. Frozen erythrocytes from the domestic chickenGallus galluswere thawed and used as an internal reference for simultaneous analysis with grass carp samples. The nuclear DNA content of erythrocytes from diploid grass carp (mean ± SD) was 2.00 ± 0.01 pg/cell, whereas triploids possessed 2.97 ± 0.03 pg/cell. Variations in the nuclear DNA content ofdifferent chickens were standardized in relation to the DNA content of fresh human leukocytes (7.00 pg/cell). The value for DNA content of the chicken erythrocytes (around 2.5 pg/cell) occupied a position intermediate between the two grass carp values, and thus provided a clear reference for discrimination between diploids and triploids.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0713:CEAAIR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Cold tolerances of juvenile blue tilapiasOreochromis aureusat salinities ranging from 0 to 35%o were determined in the laboratory by decreasing temperatures 1°C/d until fish died. Fish maintained in isosmotic media (11.6%o) survived at lower temperatures than those in water ofhigher or lower salinity. Therefore, the potential range of this exotic species in North America can be expected to extend farthest north in estuarine habitats. Inasmuch as the difference in thermal tolerance between blue tilapias in fresh water and those in isosmotic media was small (about 1°C), the additional habitable range may also be relatively small.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0718:EOSOCT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-118.6.721

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor