摘要:

Results of pond studies indicated that the number of young-of-the-year (age-0) largemouth bass Micropterus salmoides that grow to 15 cm or longer depends on the presence of suitable prey such as bluegills Lepomis macrochirus and gizzard shad Dorosoma cepedianum. Prey availability, which influences growth and length distributions of young largemouth bass, may be a major determinant of recruitment to adult stock. On the premise that large age-0 fish have lower mortality rates than small members of the same cohort, we applied a model of size structure to the problem of forecasting eventual recruitment from cohorts of young largemouth bass. The model confirmed that length distributions of age-0 fish can have important influences on subsequent recruitment; good first-summer growth may mitigate, in part, such detrimental events as water-level fluctuations. The model may be a more refined predictor of recruitment than density of age-0 fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<317:IOBSTT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Alewives Alosa pseudoharengus collected in southeastern Lake Michigan from October 1979 to October 1981 were analyzed for caloric content, lipid, and lean dry (lipid-free) weight. The relative seasonal change in energy density (kcal/g wet weight) was similar in adults and immature fish, although immatures generally had lower caloric equivalents. Seasonal lows in caloric equivalents occurred in April for immature fish in their first year (1.03 kcal/g) and in June for adults (1.30 kcal/g), whereas maxima were found in October for all age groups (2.30 kcal/g). Somatic energy losses during winter were 27% for adult females and 23% for males; spawning-related losses were higher (37% and 45%, respectively). Percent lipid followed the same seasonal trends as caloric equivalents with maxima in the fall (17% wet weight) and minima in late spring-summer (3–5%). Approximately 80% of gonad growth and maturation took place from April to late May when feeding was at a minimum. Energy requirements for gonad growth apparently came mainly from body lipid, although body protein also was used. Most body growth occurred in the fall. Seasonal increases and declines in growth were related to food availability, temperature, and spawning. Annual die-offs correspond with seasonal energy lows, indicating that mortalities may be induced by insufficient feeding the previous fall.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<328:SEDOTA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

When spot Leiostomus xanthurus larvae began to feed (age 3 d at 24°C, 4 d at 22°C, 5 d at 20°C, 5–6 d at 18°C), little endogenous energy was available to them. If food was withheld 3 d or more, most larvae died even if food then became available. Larvae were equally vulnerable to starvation throughout the preflexion stage (≤3.8 mm standard length, the stage occurring before the upward flexion of the notochord tip). Later-stage larvae (flexion and postflexion, during and after notochord flexion, respectively) survived food deprivation significantly longer than preflexion-stage larvae. Discriminant analysis of six body measurements (standard length, head length, eye diameter, body depth at anus, body depth at cleithral symphysis, body depth at pectoral fin base) identified significant changes in larva body shape during starvation and successfully classified larvae according to nutritional condition. Moderately starved and starved (food withheld for 1–2 and 3–4 days, respectively) preflexion larvae were morphologically similar, indicating that the effects of starvation proceeded rapidly. Fed and moderately starved (food withheld for 1–4 days) flexion-postflexion larvae were morphologically similar, indicating that starvation of older larvae proceeded more slowly. The proportion of preflexion larvae correctly classified improved when starved and moderately starved fish were combined into a single category (83% correctly classified); classification of flexion-postflexion larvae improved when fed and moderately starved fish were combined (87% correct).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<338:MIONCA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The effects of being towed in a plankton net on the morphometry and dry weight of Pacific herring larvae Clupea harengus pallasi were measured for groups of fed and starved fish preserved immediately in 2% formalin after a towing treatment. Towing caused significant decreases in standard length and dry weight, no change in eye diameter, and significant increases in body depth at the anus, body depth at the pectoral girdle, and head width. The changes decreased in magnitude with increasing age and size of the fish, and they are extrapolated to become nonsignificant for larvae longer than 14.0 min. The effect of the towing treatment was independent of the duration of the tow and there was no significant interaction between feeding status (starved or fed) and towing treatment. These changes in body dimensions cause significant increases in the apparent condition factors. The morphometry and dry weight of small fish larvae must be corrected for the effects of net capture before they can be used to accurately measure the nutritional status of the fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<348:EONCOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Southern kingfish Menticirrhus americanus were caught from Cape Fear, North Carolina, to Cape Canaveral, Florida, during seasonal stratified random trawl surveys. Maximum frequency of occurrence and abundance occurred in this area during summer and fall surveys. Analysis of marginal increments on scales showed annulus formation occurred from winter through early spring. Back-calculated mean total lengths at age produced von Bertalanffy growth equations of Lt= 292{1 - exp[-0.6369(t - 0.0045)]} for males and Lt= 477{1 - exp[-0.2742(t + 0.2813)]} for females, where Lt= total length (mm) at age t (years). Spawning takes place from April through August in the South Atlantic Bight, most intensively from April through early June. Southern kingfish mature at age 1. In South Carolina, 96% of the kingfish landed as by-catch from the penaeid shrimp fishery were southern kingfish, which averaged 23 cm total length (range, 18–36 cm); 81% of these were age 1 and 79% were females. Research catches indicated annual mortality rates of 67–79%, whereas commercial catches implied a rate of about 87%; the higher rate is related to culling operations at sea.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<356:BOTSKI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This report describes the age, growth, and reproductive biology of the spiny dogfish Squalus acanthias off the northeastern U.S. Analysis of growth rings on dorsal fin spines yielded yon Bertalanffy growth coefficients (K) and asymptotic total lengths (L∞) of K = 0.1481, L∞= 82.49 cm for males, and K = 0.1057, L∞= 100.5 cm for females. Median lengths and ages at maturity were 79.9 cm and 12.1 years for females and 59.5 cm and 6.0 years for males. The average number of young for females at the modal size range (90–94 cm) was 5.8; litter size ranged from 1 to 15 embryos every 2 years.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<367:LHOSDO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The ichthyofauna of the Plata River Basin (Argentina, Uruguay, Paraguay, Brazil, Bolivia) consists mainly of illiophagous (mud-eating) and detritivorous species. The primary productivity of phytoplankton is generally low. Regressions of ichthyomass and catch per unit effort against total organic nitrogen, total organic carbon, and other variables indicate that much of the spatial variability in fish abundance is explained by the content of the organic matter in the water column. These relationships are demonstrated for the Middle Paraná River and for the Salto Grande Reservoir on the Uruguay River. More limited evidence suggests that water column organic matter influences fish distribution elsewhere in the basin as well, and may account for the higher average fish abundance at the mouths of tributary rivers and streams of the Paraná and Uruguay rivers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<377:FARTOM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

I examined how constant reduced discharge influenced emigration, abundance, growth, production, and distribution of underyearling rainbow trout Salmo gairdneri in small, seminatural experimental streams in New Zealand. Three stream channels had constant discharges of 0.125 m3/s from mid-November (spring in southern hemisphere) to mid-February. Discharge was then reduced in two channels, but remained unchanged in the third. Reduction of discharge by 32% (to 0.085 m3/s) and by 60% (to 0.050 m3/s) caused no increase in downstream emigration, the emigration rate immediately before reduction being 0.1–0.7 fish/d and that for 5 months after reduction being 0.0–0.3 fish/d. However, the results may have been influenced by unequal population sizes in the channels before the discharges were altered. Presumably, these differences were caused by unequal hatching success of eggs planted in the channel substrates. Population density was greatest (41/100 m2) in the channel selected for lowest discharge and least (19/100 m2) in the channel selected for control discharge. Following discharge alteration, this pattern continued (lowest discharge: 21/100 m2; control: 7/100 m2). Fish size differences between channels at the end of the experiment (7 July) were in direct relation to channel discharges and in inverse relation to population density (largest fish in the control and smallest fish in the low discharge channel). Reductions in instantaneous growth rates were attributable to reduced discharge, but occurred about 2 months after discharge reduction. Reduced discharge depressed production after about 1.5 months and by the end of the experiment there had developed a direct relationship between discharge and production; production was 1.4 g/100 m2at 0.125 m3/s and -3.8 g/100 m2at 0.050 m3/s. There were no significant differences among the channels in the distribution of fish among riffle, pool, and run habitat types. Before discharge reduction, fish in all channels occurred mostly in the riffles and, after reduction, fish in control and treated channels became progressively more evident in the pools. Discharge reduction had no effect on this distribution.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<388:EORDOP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A stamina tunnel was used to determine the prolonged swimming performance of age-0 humpback chubs Gila cypha, bonytail chubs G. elegans, and Colorado squawfish Ptychocheilus lucius and of subadult Colorado squawfish. The “fatigue velocity” in body lengths per second at which 50% of the test fish were fatigued (FV50) was determined at 14, 20, and 26°C. The ranges of FV50 values for the three fishes (average total length in parentheses) were: Humpback chubs (95 mm), 4.4–5.7; bonytail chubs (99 mm), 4.7–5.8; small Colorado squawfish (104 mm), 4.0–4.5; large Colorado squawfish (432 mm), 2.0–2.3. Absolute speed of large Colorado squawfish was about 2.4 times that of small Colorado squawfish. Swimming ability of the subyearlings increased with increased water temperature. These rare fish had prolonged-swimming abilities similar to other fish species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<397:SPOTRC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In an acute lethality toxicity test, organisms are continuously exposed to each of several concentrations of the toxicant and subsequent deaths are recorded. The results of the test are often summarized by the toxicity curve, which shows for each concentration the exposure time required to cause exactly 50% mortality. This paper presents a new statistical procedure for estimating the toxicity curve. It is based on a mathematical model derived from plausible assumptions about the biological mechanisms of acute toxicity. The statistical fit of the model is accomplished by nonlinear, weighted, least-squares regression, estimated median survival times being responses and concentration being the independent variable. The usual methods for constructing a toxicity curve are encumbered by at least one of two weaknesses: Either the mathematical form of the curve has no apparent biological justification or the statistical fit of the curve treats concentration as the response and time as the independent variable, thereby reversing the cause-effect relationship. The new method possesses neither of these deficiencies. Analyses of two toxicity tests indicate that the proposed mathematical model is not inconsistent with real data.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<403:TCE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor