摘要:

Atlantic salmon,Salmo salar, were censused each spring and fall for 5 or 6 yr in two lakes at the headwaters of the Gander River, Newfoundland. Density, biomass, and age varied seasonally and annually, ranging from 5.2 to 78.7 fish∙ha−1, 0.2 to 3.4 kg∙ha−1, and 1 to 7 yr, respectively. Seasonal changes in age composition were used to calculate net numbers and ages of fish moving into and out of the lakes. Population sizes typically increased from fall to spring as young fish moved into the lakes from downstream spawning areas and decreased from spring to fall as older fish moved downstream. The calculated net number of spring to fall emigrants over 6 yr was positively correlated (r = 0.835) with adult abundance (catch per unit effort) in the recreational fishery 1 yr later. The varying modal age of these emigrants was identical to the modal freshwater age of returning adults in each of four comparable years. Censusing of young Atlantic salmon in standing waters can be used to monitor smolt production and assist in prediction of the subsequent abundance of sea-run adu

ISSN:0706-652X    

DOI:10.1139/f86-001

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Larval development, adult size, and fecundity ofLeptophlebia intermediawere assessed in response to rearing on five diets (hickory, white ash, red oak, chestnut oak, and American beech leaves) at each of three temperature regimes (ambient White Clay Creek temperatures (WCC) and 3 and 6°C above WCC). Developmental time was shortened about 40–50 d by elevating creek temperatures 6 °C, but varied only about 20–30 d over the range of diets for any given temperature. Adult size was influenced more by diet than temperature. Adult female weights differed among diets by about 1.5 mg for any given temperature regime. In contrast, female weights varied by only about 0.6 mg among temperatures for any given diet. The proportion of total female weight allocated to eggs increased with adult size and ranged from 0.12 to 0.45 depending on diet and temperature. In general, hickory and white ash diets consistently yielded the highest survival and largest adults, while the highest mortality and poorest growth occurred on the red oak and American beech diets.

ISSN:0706-652X    

DOI:10.1139/f86-002

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Oxygen uptake attributable to apparent heat increment (AHI) in rainbow trout,Salmo gairdneri(10–15 g), induced to swim atwas influenced by dietary energy intake and diet composition. Twelve balanced diets were tested, with protein levels of, 40, 48 and 60% and lipid levels of, 15, and 23% factorally combined. Diets supplying 34% protein and 23% lipid (protein to energy ratio of 94.3 mg∙kcal−1) resulted in the lowest AHI of all diets tested, indicating most efficient utilization of dietary protein. At a dietary lipid level of 23%, dietary protein levels lower than 34% may result in a further reduction in AHI. Duration of elevated metabolism following feeding was independent of dietary protein and lipid level, as well as dietary energy intake. AHI of rainbow trout represented the equivalent of 15–24% of the digestible energy intake, depending on diet composition. A reduction in dietary protein with a concomitant increase in dietary lipid in the formulation of feeds for aquaculture purposes could enhance growth efficiency by reducing the energy expenditure for AH

ISSN:0706-652X    

DOI:10.1139/f86-003

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Morphological and histologial studies demonstrated that estrogens and androgens affect sexual differentiation and can be used to control the phenotypic sex of yellow perch (Perca flavescens). Normal perch larvae of 5–10 mm total length (TL) had paired gonads with no sex-distinguishing features. In normal 16 mm TL perch, the gonads of females had fused into a single sac-shaped organ, while in males the gonads remained paired. Oogenesis had begun in most females of 35 mm TL. Spermatogenesis in males and vitellogenesis in females were first observed at 85 mm TL. Treatment (for 84 d) of perch (initially 20–35 mm TL) with estradiol-17β at 15–120 μg/g diet induced complete germ cell sex inversion in most males. Similar treatment with 17α-methyltestosterone at 1.5 to 60 μg/g diet induced spermatogenesis and the formation of ovotestes in females. Sperm collected from such ovotestes fertilized normal ova, and the resultant offspring were all female. Our findings indicate that in yellow perch: (1) differentiation of the somatic elements of the gonads precedes gametogenesis, (2) gametogenesis begins earlier in females than in males, (3) the attainment of a specific minimum body size (80–100 mm TL) is important to the initial onset of vitellogenesis and spermatogenesis, (4) both estrogens and androgens are probably involved in mediating sexual differentiation of germinal tissues and (5) females are the homogametic sex.

ISSN:0706-652X    

DOI:10.1139/f86-004

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The lesions observed in channel catfish (Ictalurus punctatus) as a consequence of exposure toEdwardsiella ictalurivia gut and water were studied. Channel catfish fingerlings were exposed to 1010bacterial cells via the gut and placed in tanks with unexposed fish. Both groups of fish were sampled periodically over a 35-day period. The gut-exposed fish exhibited gross signs of a systemic infection within 2 wk. Enteritis, hepatitis, interstitial nephritis, and myositis, all of which began as acute reactions and developed into chronic lesions, were observed histologically. Some of the contact fish developed systemic infections beginning in the intestine, thus demonstrating horizontal transmission. However, only contact fish developed the characteristic "hole in the head" lesion, which began in the olfactory sac and progressed to a granulomatous meningioencephalitis. These results indicate that both gut and nares are sites of primary infection in natural outbreaks ofE.ictaluri.

ISSN:0706-652X    

DOI:10.1139/f86-005

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The effects of chrysotile asbestos on siphoning activity, shell and tissue growth, fiber uptake, and gill ultrastructure in adult Asiatic clams (Corbiculasp.) and on larval release and mortality patterns from reproductively active adults were evaluated in 96-h to 30-d experiments at 0–108fibers/L. Adult siphoning activity was significantly (α = 0.05) depressed in 96-h asbestos exposures when no food was offered or after 30 d when food was available. Shell growth was significantly inhibited in accordance with reduced siphoning.Corbiculaexposed to 108fibers/L accumulated 69.1 fibers/mg dry weight if food was offered. Fiber uptake was not observed at lower concentrations in 96-h or 30-d tests. Adult clams exposed to 108fibers/L for 30 d accumulated 147.3 and 903.7 fibers/mg in gill and viscera, respectively. Gill tissue was significantly altered at 108fibers/L and fibers were observed in gill locules and in ctenidial tissue. Fiber dimension analysis suggested that small, thin fibers were preferentially accumulated by both gill and visceral tissues. Significant increases in mortality of larvae exposed to asbestos and decreases in larvae released per milligram of adult dry weight were observed in reproductive adults exposed to asbestos at 104–108fibers/L.Corbiculais an efficient accumulator of chrysotile asbestos and may be considered for use as an indicator of asbestos contamination.

ISSN:0706-652X    

DOI:10.1139/f86-006

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Difficulties in producing a muddy substrate which does not easily foul have made previous efforts to culture mud-inhabiting, estuarine, and marine harpacticoid copepods unsuccessful. Natural, organic-rich muds are unsuitable as a long-term culture medium because they generate detrimental bacterial blooms in stagnant and periodically flushed culture systems. I present some simple procedures to (1) sort muddy sediments into a <125-μm size class, (2) flush away most dissolved organics, (3) sterilize the sediments providing a moderately foul-free culture medium, (4) generate a life-like, flocculent surface layer, and (5) allow easy observation above or below the sediment surface. Five harpacticoids were cultured within 45–90 d to densities 4–11 times their natural field maxima (per 10 cm2):Scottolana canadensis(372),Paronychocamptus huntsmani(380),Onychocamptus mohammed(448),Cletocamptus deitersi(1259), andNitocra lacustris(1662). Since most mud-inhabiting harpacticoids are larger than 125 μm, simple sieving on a 125-μm screen eliminates culture sediments leaving behing hundreds of clean, easily collected harpacticoids.

ISSN:0706-652X    

DOI:10.1139/f86-007

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Radiotracer experiments were carried out in 20 enclosures located in two lakes at the Experimental Lakes Area (ELA), northwestern Ontario, to study pathways of trace metal removal from the water column of shallow lakes. Two removal mechanisms were characterized: (1) sorption to and subsequent transport with falling particles and (2) direct adsorption to surface sediments. Our approach was to measure independently the kinetics of radiotracer sorption, fluxes and concentrations for particles, particle settling velocities, and the "equivalent stagnant boundary film." Our radiotracer results enabled us to test the sensitivity of the tracer removal rates on these rate-determining processes using a numerical transport model. Acid titrations of whole ecosystems revealed that some trace metals (e.g. Mn, Co, and Zn) can diffuse back to the water column as the pH is lowered from 6.5 to 4.8 after 18 d, while others remain tightly bound (e.g. Sn, Fe, Se, Cr, Ag, and Hg isotopes). Subsequent CaCO3additions to bring back the pH to its original value restored the initial removal conditions for acid-sensitive radiotracers, indicating that the pH sensitivity is reversible. Transport parameters for particle-related pathways or diffusive pathways across the sediment–water interface obtained from our enclosure experiments were used to predict the removal rates of "particle-reactive"60Co and the "diffusive" pathway tracer134Cs observed in earlier experiments where radiotracers were added to whole lakes or to larger enclosures.

ISSN:0706-652X    

DOI:10.1139/f86-008

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The possible effects of tidal amplitudes altered by Fundy tidal power development upon potential fish production in the Gulf of Maine are examined with a marine ecosystem model. Three areas off the Maine coast are delineated on the basis of winds, tides, and the extent of vertical mixing. An optimum kinetic energy from wind and tide exists for maximum primary production in the water column. Primary production in the model is the base for a simple pelagic food chain leading from phytoplankton through zooplankton to fish. If the construction of a tidal power dam in the upper Bay of Fundy results in a 5–10% increase in tidal amplitude, our first-order model predicts that enhanced vertical mixing from May to October will increase potential fish production along the Maine west coast by 7–12%. Fish production along the Maine east coast and in offshore waters is predicted to remain at present levels. Climatic variation is predicted to have as large an impact on fish production as man-induced changes in vertical mixing caused by tidal power development.

ISSN:0706-652X    

DOI:10.1139/f86-009

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A linear programming (LP) approach to effort allocation among two or more fisheries (fleets) exploiting several common species/stocks is described and applied to otter trawl fisheries exploiting demersal fish stocks on Georges Bank (northeastern United States). Total instantaneous fishing mortality on a particular species (i) is computed as the linear summation of fishing mortalities generated by each fishery (j):wherefjis the amount of standardized fishing effort exerted in fisheryjandqijis the catchability coefficient for speciesitaken in fisheryj. Mortality on speciesidue to both directed fishing and by-catch can thus be accounted for in theqij's. Optimal allocation of effort among thejfisheries may be considered a minimization problem (minimize Σfj), subject to the constraints that fishing mortality rates on particular species are maintained at, above, or below certain predefined levels. Fishing mortality goals for individual species can be based on various biological and/or economic criteria: fishing mortality rates that prevent growth or recruitment overfishing, or that optimize productivity from predator–prey systems. Other constraints in the LP model may be included to modify optimal solutions based on various economic and social considerations (e.g. protection of certain fisheries). Sensitivity analyses indicate the general infeasibility of maintaining relatively high or low fishing mortality rates on ubiquitously distributed species, while moderately fishing species with more discrete distributions, due to by-catch considerations.

ISSN:0706-652X    

DOI:10.1139/f86-010

出版商:NRC Research Press    

年代:1986

数据来源: NRC