摘要:

Ctenopharyngodon idella (grass carp) and Aristichthys nobilis (bighead carp) have a diploid chromosome number of 48 with no acrocentric chromosomes. The hybrid of these species is triploid with 72 chromosomes. The frequencies of metacentric and submetacentric chromosomes suggest that the hybrid receives two maternal and one paternal set of chromosomes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<433:KAOCIA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Heritability estimates and genetic and phenotypic correlations were determined for length and weight at 45 and 90 days in the Auburn strain of Tilapia nilotica. Heritability estimates were determined by half-sib analysis from an experiment that contained 16 paternal half-sib families or 32 full-sib families, that is, two full-sib families nested in each of 16 paternal half-sib families. Average length and weight were 63 mm and 4.9 g at 45 days, and 99 mm and 18.6 g at 90 days. Sire heritability estimates ranged frown 0.04 to 0.10, and dam heritability estimates ranged from −0.02 to 0.54. Dam heritability for length at 45 days was the only heritability estimate that was significantly different frown zero (P = 0.05). At 45 days, environmental and dominance genetic variance were the major contributors to phenotypic variance, while at 90 days environmental variance accounted for virtually all of the phenotypic variance. Genetic and phenotypic correlations between length and weight at 45 and 90 days ranged from 0.94 to 1.12. Predicted gains from mass selection were small because of low heritabilities and small standard deviations. Low genetic variation may have been caused by drastic reductions in the effective breeding number during transfer of the fish stocks from the Ivory Coast to Brazil and from Brazil to Auburn. Problems caused by reduction of genetic variance as a result of reductions in effective breeding number are discussed.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<439:PRTSFE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Channel catfish (Ictalurus punctatus) were stocked in 0.02- and 0.04-hectare ponds at 20,385 fish per hectare and fed daily. Fish averaged 11 cm total length and 6.2 g at stocking. Six ponds received nightly aeration (2 to 6 hours) and six ponds received no aeration. A maximum feeding rate of 90 kg/hectare was reached in October. In aerated ponds, no dissolved oxygen (DO) problems occurred, and survival was 92%. Fish mortalities resulted from DO depletion in all unaerated ponds, and survival was 40%. Nitrite-nitrogen concentrations were significantly higher in the aerated ponds, though never at levels reported as lethal to channel catfish. Concentrations of un-ionized ammonia were high enough in both aerated and unaerated ponds to have adversely affected growth. Aerated ponds yielded an average of 5,307 kg/hectare of channel catfish and had a net economic gain of $1,500 per hectare. The unaerated ponds yielded an average of 1,400 kg/hectare and were an obvious economic failure. Direct extrapolation of economic data to large commercial ponds is not advised.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<446:NATIPO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Lack of spawning areas limits standing crops of brook trout (Salvelinus fontinalis) in many small, spring-fed ponds in northern Wisconsin. A new method for developing spawning areas includes measurements along pond shorelines of hydrostatic head (an index of upwelling groundwater) and particle size of mineral soils to screen potential development sites. Organic overburdens were excavated from sites with appropriate groundwater characteristics and coarse mineral soils. Brook trout constructed redds in both natural and developed sites where seepage velocities ranged from 11.5 to 45.0 cm/hour and about 45% of the substrate, by weight, averaged less than 2 mm in diameter. Because the hydrostatic head in excavated and natural spawning areas was similar, seepage velocities, hence locations of redds, were determined by substrate permeability. Spawning-site development contributed to increased recruitment of juvenile brook trout in two of three study ponds.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<453:FOSSSD>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Pink salmon (Oncorhynchus gorbuscha), introduced into Lake Superior in 1956, were believed to have a 2-year life cycle and spawn only in odd-numbered years. We collected 28 even-year spawners from three Lake Superior tributaries in 1978. Scale examination and the large size (as compared to 2-year-old salmon of the same year class) proved that at least 21 of the 28 were 3-year-old pink salmon. Only three such salmon have been reported previously from North America.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<458:TPSILS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Rainbow trout (Salmo gairdneri) were exposed to various combinations of water hardness, pH, and copper. Hematocrits of exposed fish were measured after the fish were fatigued by forced swimming. In the absence of copper, hematocrits were not significantly altered by hardness and pH. In pH 6.0, hematocrit increased with increasing copper exposure. At pH 7.9, this response to copper was evident only at a hardness of 30 mg liter-1. Data on red blood cell counts, and carcass and muscle moisture suggest that hemoconcentration was accompanied by a shift in water from blood to muscle.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1980)109<461:CIHORT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/00028487.1980.10493207

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor