摘要:

A survey of 500 studies published between 1907 and 1980 that included estimates of fish age indicated that only 65% mentioned age validation or attempted to validate the ageing technique. In less than 3% was the technique validated for all age classes. Among the 35% that did not consider age validation, many did not consider the possibility that ages may be incorrect. Among 75 additional publications published in primary journals between 1965 and 1980 that assessed stock dynamics and used fish ages, only 40% mentioned or attempted age validation, and none successfully validated all age groups used in the analysis. Many investigators continue to neglect the critical study of age validation despite the clear direction of the early work on age determination. We show that estimated ages greater than the maximum validated age must not be considered accurate. Use of inaccurate ages has caused serious errors in the management and understanding of fish populations. Only by mark-recapture studies or use of known-age fish can all age classes in a population be validated. If such studies are not possible, fish should be aged by several methods, and the possibility of errors in age estimates must be considered.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<735:TFRFAV>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Historical catch data on American lobsters Homarus americanus from the Canadian Maritime Provinces and Maine were examined for stock differences with the object of defining lobster population boundaries. Pattern-recognition techniques (cluster analysis and principal-component analysis) applied to 1892–1981 lobster landings from 32 areas and reviews of the literature support the hypothesis that there are at least three main stock areas: (1) western Maritimes (Gulf of Maine), including Maine, the Bay of Fundy (inshore and offshore), and southwestern Nova Scotia; (2) the eastern coast of Nova Scotia (Queens to Richmond Counties), which seems to be a transition zone for lobsters between the Gulf of Maine and the Gulf of St. Lawrence; and (3) Gulf of St. Lawrence, which can be subdivided into six areas whose landings were clustered separately, but also loosely linked together.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<744:DOALSF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Redd-substrate composition, water velocity, depth, and other environmental variables associated with redd-site selection and spawning by brook trout Salvelinus fontinalis and brown trout Salmo trutta in southwestern Ontario streams were examined. Sympatric and allopatric populations spawned in similar ranges of specific conductance (225–810 μmhos/cm), pH (7.0–8.2), dissolved oxygen (>83% saturation), and stream gradient (0.2–2.3%). Brook trout spawned exclusively in areas of groundwater seepage, typically near headwaters where streamflow did not exceed 177 litres/second. Brown trout spawned in a wider range of flows (21–600 liters/second), and utilized locations with and without groundwater seepage. Spawning by brook trout usually began by the second week of October, by brown trout a week later. Brook trout spawning periods lasted 3–5 weeks, those of brown trout, 2–4 weeks. In sympatric populations, an overlap in spawning time occurred for up to 3 weeks. Reuse of redds was mostly intraspecific, although interspecific reuse of brook trout redds by smaller brown trout did occur, particularly below barriers to upstream movement. Mean water depth over redds selected by brook (24.0 cm) and brown trout (25.5 cm) were similar (P > 0.05). However, mean stream velocities were significantly (P < 0.001) slower at brook trout (17.6 cm/second) than at brown trout redds (46.7 cm/second). Average geometric mean sediment size of brook trout redds was significantly smaller than that of brown trout redds (5.7 mm versus 6.9 mm; P < 0.02), but less well sorted. Redd-site preference by brook trout for areas of groundwater seepage and by brown trout for faster water velocities and coarser substrates minimized species interactions during spawning. Larger body size of mature brown trout (18.0–54.5 cm fork length) than of mature brook trout (8.4–29.0 cm) was probably a factor in the brown trout's ability to utilize faster currents where coarser gravels were found.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<760:RSBBTA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The influence of supplementary forage on home-range size of largemouth bass Micropterus salmoides was studied via radio-telemetry. Largemouth bass were caught in Cedar Lake, Illinois, tagged, and released back to the lake either at an experimental feeder from which fathead minnows Pimephales promelas escaped at a rate of 10/hour or at a control feeder that never contained prey. Three largemouth bass released at the experimental feeder established home ranges that included the feeder. These home ranges were significantly (P = 0.05) smaller than the areas utilized by three largemouth bass released at the control feeder, and significantly (P < 0.05) smaller than natural home ranges for largemouth bass in the lake. The home ranges of fishes at the experimental feeder were 0.05, 0.09, and 0.10 hectares; fish released at the control feeder utilized areas of 1.27, 6.10, and 70.47 hectares. After the stocking of supplementary forage was stopped, two largemouth bass at the experimental feeder increased their home-range size from 0.10 to 0.79 hectares and from 0.05 to 7.17 hectares, and the other was never located again.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<772:EOFOHS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Grass carp Ctenopharyngodon idella (50/hectare) were introduced into three central-Florida lakes with dense infestations of the aquatic macrophyte hydrilla Hydrilla verticillata; aquatic vegetation and water quality were monitored for 43 months. They also were introduced (61/hectare) into a north-Florida reservoir with dense populations of Illinois pondweed Potamogeton illinoensis and Eurasian watermilfoil Myriophyllum spicatum; aquatic vegetation and water quality were monitored for 48 months. In the three central-Florida lakes, the hydrilla has remained absent for 6 years and is possibly eradicated. The only remaining plants are either in very shallow water, woody plants, or unpalatable species such as spatterdock Nuphar luteum. In the north-Florida reservoir, the Illinois pondweed was eliminated 2 years after the initial stocking and the Eurasian watermilfoil was greatly reduced 3 years after stocking. The reduction of Eurasian watermilfoil lasted 3 years and the Illinois pondweed remained absent 8 years after grass carp were stocked. Turbidity increased in all four lakes; chlorophyll α decreased significantly in three lakes and exhibited no significant changes in the fourth. Three lakes exhibited long-term increases in nutrient-related variables: Kjeldahl nitrogen in two central-Florida lakes and the north-Florida reservoir, orthophosphorus in two central-Florida lakes and total phosphorus in one central-Florida lake. The least-developed (for human habitation) and deepest central-Florida lake experienced initial increases in Kjeldahl nitrogen, orthophosphorus, and nitrate-nitrogen, but these variables returned to baseline levels in subsequent years. Nitrate nitrogen decreased in the north-Florida reservoir and one central-Florida lake. The degree of lake enrichment by grass carp feeding activities probably is related to nutrient loading, water depth, and the reduction of the nutrient buffering capacities of the submersed and marginal plant communities.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<777:EOVCBG>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Adult spawning behavior and emigration of larvae of the endangered cui-ui Chasmistes cujus were studied in a natural side channel of the lower Truckee River. External radio-tags placed on eight apparently did not affect spawning behavior. Cui-uis spawned in clusters of two to seven fish; usually a single female was flanked by two males. Each spawning act lasted 3–6 seconds, and individual fish spawned numerous times. The most active tagged male and female spawned at least 294 times and 114 times, respectively. Individual females broadcast eggs over an area of up to 50 m2. Males spawned over a 4–5-day period, and females over 2.5–4 days. Most spawning occurred at night in water depths ranging from 9 to 43 cm, water velocities ranging from 23 to 87 cm/second, and temperatures of 12–17 C. The preferred spawning substrate was gravel. Peak emergence and out-migration of cui-ui larvae occurred 14 days after peak spawning.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<788:RBTECI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The phenol tolerances of three Alabama populations of mosquitofish Gambusia affinis were compared; two populations lived in industrially polluted streams and one in a nonpolluted lake. In 48-hour static tests, the median lethal concentration (LC50) of phenol was significantly higher for mosquitofish from a stream that received coke-treatment wastewater from a steel plant than for the other two populations. Especially at low phenol concentrations, most mortality occurred during the first few hours of exposure, indicating that some individuals were much more susceptible to phenol than others. Eight-hour assays of fish from the lake and the most polluted stream confirmed the presence of distinctly phenol-resistant and phenol-susceptible groups of fish. The differences in LC50 values for these two populations reflect differing proportions of resistant individuals. Resistant fish made up 67–80% of the polluted-stream population with the high LC50 and only 23–27% of the nonpolluted-lake population. Repeated nonlethal toxicity tests on individuals demonstrated that some fish are invariably susceptible and others show resistance at some times and susceptibility at others. Phenol resistance apparently depends on the induction of a genetically determined, rapidly acting detoxification mechanism.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<794:PTIPOM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Yearling coho salmon Oncorhynchus kisutch acclimated to fresh water or seawater were subjected to severe chronic confinement stress in fresh water, seawater, or a medium (one-third-strength seawater) that was approximately isosmotic to the fish's blood. Plasma osmolarity, Na, K, Ca, Mg, and cortisol and blood hematocrit were measured in fish sampled at 1, 7, 24, and 48 hours after stress began. Plasma osmolarity and electrolyte concentrations increased during stress in seawater, but generally decreased during stress in fresh water. Osmotic imbalance did not occur in fish that were stressed in one-third seawater. Hematocrit increased in fish stressed in fresh water and decreased in fish stressed in seawater. Fish acclimated to fresh water tended to regain osmotic balance within 48 hours when stressed in fresh water, but in seawater they died. Fish acclimated to seawater tended to regain osmotic balance within 48 hours when stressed in seawater, but in fresh water a compensatory trend was not evident. Confinement stress greatly amplified the osmotic imbalance after fish were transferred from fresh water to seawater compared with that in unconfined fish. Plasma cortisol concentrations increased during stress for all groups; however, fish stressed in one-third seawater had lower concentrations of cortisol than the other groups within 7 hours after stress began.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<800:IOASOO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Twenty-six morphological and meristic characters of diploid and triploid hybrids between female grass carp, Ctenopharyngodon idella and bighead carp Hypophthalmichthys nobilis were analyzed by discriminant-function analysis. Twelve characters were useful in distinguishing between diploids and triploids. When these 12 characters were subjected to discriminant-function analysis, 97% of the hybrids were correctly classified as either diploid or triploid. No single character allowed diploids to be distinguished from triploids. Triploid hybrids had fewer morphological abnormalities than did diploid hybrids, possibly because triploid hybrids had two sets of chromosomes from the same species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<808:POHBGC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

In a 12-week growth study of the dietary requirements of young lake trout Salvelinus namaycush for essential branched-chain amino acids, the leucine requirement was between 2.74 and 3.66%, and the isoleucine requirement between 1.54 and 2.06%, of dietary protein (as-fed basis). These ranges are substantially lower than those published and widely used in formulation of salmonid feeds. On the basis of both growth criteria and concentration of free amino acids in blood plasma, the valine requirement was within the range of 1.77 to 2.23% of dietary protein. The upper value of this range is substantially lower than the requirement reported for chinook salmon Oncorhynchus tshawytscha. Plasma valine concentrations in lake trout responded to dietary supplements of valine above the requirement level; the concentrations increased sharply once the requirement was exceeded. This finding is similar to observations recorded in other animals.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<812:DRFEBA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor