摘要:

Newly hatched larvae of the cyprinid Leuciscus leuciscus in the River Frome, England, commenced feeding on rotifers and diatoms but expanded their repertoire to copepods, cladocerans, and chironomids as they grew. Daytime gut contents averaged 3–4 times the volume present during 0200–0600 hours. A detailed study was made of gut-content variation among 3-week-old larvae from four backwater sites; each river site was sampled 10 times in 31 h. Forty-seven percent of variation in food volume was attributable to differences between individual larvae at the same site and time. The remaining variation was due principally to differences among sites (22% of variance) and sampling time (24%). Variation in gut prey assemblages was due mainly to among-site differences although time and site x time interactions also contributed significant amounts of variance. These results indicate the importance of rigorous sampling strategies and analysis in characterising larval diets. Data generated from a single time or particularly from a single site cannot be reliably applied to a wider context.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<519:SOVITF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Postemergent larval grayling (15–28 mm fork length) were sampled from the River Frome, Dorset, between 19 April and 9 May 1983. They occupied surface waters close to river banks until they reached lengths greater than 25 mm, when they migrated to near-benthic habitats. The fish were distributed in areas where water velocity was between 3 and 9 body lengths˙s−1. While in the surface waters, the grayling fed exclusively on invertebrates drifting on or near the surface; larval, pupal, and adult chironomids accounted numerically for 80–90% of the diet. The fish ceased feeding at night and elected prey larger than 2 mm during the day. Food passed through the gut in 6.5 h when fish fed ad libitum, but took 9 h following a single meal. Comparisons of the amount of food available in the river with that consumed by the fish indicated that prey abundance was not a limiting factor to the growth of larval grayling in the River Frome during the early post-emergence period.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<525:DGAFOP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Laboratory experiments with known-age bloater larvae raised under constant photoperiod (12 h light: 12 h darkness) showed that deposition of otolith rings began at first feeding and occurred daily at all but the lowest growth rates. Based on ring counts, the age of individual bloaters could be estimated within ±6 d over the first 5 months of life. Otoliths of larvae fed high rations interrupted by 5-d periods of starvation or low rations contained obvious bands of abnormally low-contrast rings corresponding to these stress periods. The relationship between fish length and otolith diameter varied among experiments, independent of growth rate. Therefore, back-calculation of length at age will require an estimate of this relationship for each field application.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<532:EOAFBC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The influence of illumination and prey contrast on survival, growth, and feeding of larval yellow perch fed Artemia sp. nauplii was tested in an experimental upflow culture system. The treatment with high light level and high prey contrast (205 lux, black background) supported the best survival (mean, 44.2%) and growth (mean total length, 8.9 mm; mean wet weight, 5.0 mg) from hatching to age 14 d. Mean survival was 37.2% when light was low and prey contrast high (75 lux, black background). In the remainder of the tests, survival to age 14 d ranged from 0 to 6.9%. Low light and low prey contrast caused a 1–2 d delay in initial feeding. Visibility of the prey resulting from contrast with the surroundings, rather than light level, accounted for most of the variation in the ability of yellow perch larvae to acquire adequate food.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<540:EOIAPC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Burst swimming by newly emerged coho salmon from two populations was studied with electrical shock stimulation and high-speed cinematography. At emergence, Morrison Creek fish were larger (31 versus 27 mm standard length) than fish from Wade Creek. The larger fish attained greater mean and maximum burst speeds than the smaller fish and differences in swimming performance (up to 80%) were greatest over the first 0.03 s of acceleration. When exposed to 140-mm coho salmon predators, more of the larger Morrison Creek fish survived than of the Wade Creek fish. Size-mediated differences in burst swimming performance appear to be the basis for the observed difference in susceptibility to predation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<546:BSASPO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The characteristics and ontogeny of the startle response to various stimuli of laboratory-reared coho salmon were studied with high-speed cinematography. Dechorionated embyros did not exhibit a startle response to electrical stimulation; however, at hatching, the startle response could be provoked consistently (> 90% response) with electrical stimulation. After hatching, the kinematics of the startle response remained unchanged as the fish grew but the velocities attained during the response increased. The percentage of fish responding with a startle response to visual, tactile, and acoustico-lateralis stimuli was low (0–20%) at hatching, but after 3 weeks at 2°C, 50% of the fish tested exhibited a startle response to acoustico-lateralis stimulation. At this time, only 20–25% of the fish tested responded to tactile stimulation. The response to visual stimulation increased slowly up to emergence but at emergence (8 weeks after hatching) the percentage of fish responding to visual stimulation increased sharply to 75%.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<552:OOTSRI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Yolk-sac larvae of turbot from the Baltic Sea were raised at 15, 18, and 21°C in brackish water (17‰ salinity) and larvae from the North Sea were raised at 15°C in seawater (32‰). Rate of yolk utilization and growth of larvae in length and weight were monitored. Decrease of yolk weight was correlated with time and temperature, whereas the increment of larval tissue reached a peak after 2/3 of the yolk-sac phase. During the last 24 h before the larvae acquired the ability to feed, they suffered from energy deficiencies. North Sea larvae, which floated passively at the surface of full-strength seawater, consumed yolk less rapidly than Baltic Sea larvae, which sank in water of 17‰ salinity and had to swim. Yolk-utilization efficiencies (percentage of yolk energy transformed into tissue energy) were highest in seawater at 15°C (72%) and lowest in brackish waters at 21°C (51%). Efficiencies decreased with time during development under all experimental conditions.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<558:UOEESB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Early life history stages of brook trout were exposed abruptly to low pH in laboratory tests to simulate pH depressions in streams during the spring runoff; growth, development, and mortality were monitored. Eyed eggs showed delayed hatching and increased mortality during hatching at pH 5.5, compared with control eggs at pH 6.9. Posthatch growth patterns did not differ at pH 5.5 and above. At pH 5.0, however, growth of larvae was retarded in coincidence with delayed development of the gastrointestinal tract. Both growth and gut development rebounded during the juvenile stage, an indication of acclimation of the growth response to low pH. At pH 4.5, growth was curtailed and alevins suffered 100% mortality when gill filament expansion occurred at higher pHs. Biomass of treatments during the 123-d study differed as follows: Control = pH 6.5 = 6.0 > 5.5 > 5.0 > 4.5. When acidification was imposed at the alevin stage, a reduction to pH 5.0 caused immediate growth retardation, followed by a period of growth comparable to that of the control. At pH 4.5, alevins exhibited growth well below control levels throughout this experiment (26 d). Acidification at swim-up to pH 4.5 did not affect feeding behavior of larvae, but growth was retarded. Later life stages were more resistant to exposure to low pH; eyed eggs, alevins, and larvae exposed to pH 4.5 exhibited 100, 48, and 13% mortality, respectively. Acidic spring runoff is a threat to brook trout productivity in streams.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<564:GOBTSF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Fertilized steelhead eggs were water-hardened at constant pH levels of 4.0, 4.5, 4.7, 4.9, 5.1, 5.5, 6.0, 6.5, and 7.2. Water uptake was significantly inhibited (P < 0.05) at pH 5.5 and lower. The ability of eggs to resist deformation when subjected to mechanical loads was significantly reduced at pH 6.0 and lower. Eggs transferred to pH 7.2 after water-hardening at pH 4.0, 4.5, or 4.7 gained additional water but the total amount imbibed remained significantly less than that expected for constant exposure to pH 7.2. In contrast, resistance to deformation rose to values typical of continuous exposure to pH 7.2. Eggs transferred to pH 4.0, 4.5, or 4.7 after water-hardening at pH 7.2 lost small but significant amounts of water. Resistance to deformation declined more sharply to values only slightly greater than those expected for continuous acid exposure. Reductions in water content associated with initial water-hardening were irreversible. However, back-transfers indicated that pH-induced changes in water content and resistance to deformation were fully reversible once hardening was completed. Analysis of results suggests that low pH interferes with cortical vesicle exocytosis, affects the osmotic activity of perivitelline colloids, and reduces capsule strength.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<571:RWUART>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Four-week-old striped bass larvae were exposed for 24 h to 60, 80, 110, or 150/zg Cu++/L prior to an examination of their corneas by light and electron microscopy. Epithelial cells were sloughed from the corneas in a dose-dependent manner; corneas from fish exposed at the highest concentration were so denuded that the stromas were exposed. Corneas from fish exposed to 80 and 110 μg/L also exhibited a second type of pathological response that was concentration-dependent and resulted in greatly enhanced cytoplasmic density, condensed nuclear chromatin and pyknosis, extensive cytoplasmic vacuolation, and mitochondrial swelling and degeneration in the epithelial cells. Copper-induced pathological changes of the visual system may affect the ability of larvae to feed and to respond normally to visual stimuli.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<577:CDILOS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor