摘要:

To elucidate prey preferences, we quantified stomach contents of 1,231 salmonines collected from inshore (21 m or shallower) southeastern Lake Michigan during 1973–1982. Predators ate 12 species of fish. Alewife Alosa pseudoharengus made up 48–79% by weight of the diet of brown trout Salmo trutta, chinook salmon Oncorhynchus tshawytscha, coho salmon Oncorhynchus kisutch, lake trout Salvelinus namaycush, and rainbow trout Salmo gairdneri. Alewives eaten ranged from 23 to 245 mm total length; 46% were 150–200 mm. Rainbow smelt Osmerus mordax eaten were 21–245 mm long and made up 4–11% of the salmonines' prey. There were significant direct linear relationships between lengths of alewives and rainbow smelt eaten and lengths of the five predators. Alewives are currently declining in Lake Michigan. If their population collapses, there should be a shift to alternative prey species. We have seen no such shift through 1982, although more recent data of other investigators show a decline in the importance of alewife in salmonine diets. Diets of the midwater-feeding chinook and coho salmon were heavily dominated by the pelagic alewife, whereas brown and lake trout diets were more diverse. This suggests that trout should have better survival and growth than salmon, because trout would be able to utilize the more benthic yellow perch, Perca flavescens, rainbow smelt, and, to some degree, bloater Coregonus hoyi. The latter species are becoming more abundant with the decline in alewife. Under the current salmonine stocking regime, alewives will continue to supply a lower and variable portion of the salmonine diet, and predatory pressure on alewife should lead to increases in endemic prey species' populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<677:DASOMP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Seasonal patterns of age-specific growth rates and condition factors of rainbow trout Salmo gairdneri and brown trout S. trutta were studied in relation to the available food resources in five streams of the southern Appalachian mountains. Standing crops of benthic invertebrates were low relative to streams of similar size in other geographic areas. Although terrestrial organisms contributed substantially to the invertebrate drift, total drift rates were also relatively low. Numbers of prey items per trout stomach were small and were directly related to drift rate. These results reflected the limited food base. Condition factors (weight˙length-3) of age- 1 trout declined during summer, and growth rates among age-1 and older trout were generally lower in summer than in winter, despite favorable summer water temperatures. This “inverted” seasonal pattern of growth was likely due to an inadequate food base. We believe that growth rates were relatively low in summer because much of the limited energy intake was devoted to metabolism and little energy was left for growth. Higher growth rates occurred in winter because energy requirements for metabolism were reduced at lower water temperatures. An important function of habitat in food-limited streams may be to partition overall fish production among age classes by providing energy-efficient feeding sites for different sizes of fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<692:EOFLOR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Estimates of relative egg deposition and larval abundance suggest that events occurring between spawning and the first 1–2 months after hatching play a major role in determining recruitment success of bloater Coregonus hoyi in Lake Michigan. Although relative egg deposition in 1983 was only 57% of that in 1982, larval recruitment was 2.4 times greater in 1983. We investigated mechanisms governing survival of larval bloaters by comparing characteristics of individual “survivors” through the first 1–2 months of life with those of larvae at earlier life history stages. Otolith analysis was used to identify stress periods and to determine ages, first-feeding dates (close correlates of birthdate), and average growth rates of individual bloater larvae from hatching to nearly 2 months of age in 1982 and 1983. Differences between the observed distribution of first-feeding dates for newly hatched larvae and the expected distribution predicted from egg deposition showed that eggs spawned early experienced higher mortality during the incubation period than did eggs spawned later. Eggs spawned early took about 2.5 weeks longer to develop than eggs spawned later because they incubated at cooler temperatures; this prolonged exposure to mortality sources may account for the observed difference in survival. Differences between the distributions of first-feeding dates for newly hatched larvae and larvae about 1 month old also suggested that early hatching larvae experienced higher initial mortality than late-hatching larvae. Starvation was not an important cause of mortality; growth rates of all larvae collected in the field were as high as or higher than those of larvae reared in the laboratory and fed ad libitum. Larvae hatching early in the season, however, grew only about half as fast during their first 3 weeks as larvae hatched later. These early hatching, slower growing larvae were also more likely to exhibit stress marks in the otolith ring pattern during their first 2 weeks, marks that were similar to those caused in the laboratory by short periods of starvation or low ration. Lower growth rates and higher frequency of stress marks for larvae during the period of higher relative mortality suggest that size or growth-rate-dependent mortality (e.g., predation) during the first few weeks of life may be an important mechanism affecting bloater recruitment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<703:EOMRLS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In order to determine characteristics that would facilitate assignment of larvae and juvenile fish to the correct species of Morone, we examined osteological patterns and morphometric ratios of larvae and juveniles of striped bass M. saxatilis and white bass M. chrysops as well as their F1, F2, and backcross generations. Similarities in patterns of pterygiophore interdigitation between pure Morone species and their hybrids did not allow for separation based on primary pattern sequences alone. Statistical analyses of these patterns allowed for sorting of groups into subcategories but not for assignment of individual larvae to species. We corroborated pattern sequencing found by other investigators for pure-strain stocks and developed a new approach to confirming pattern-sequencing data. There was definite overlap in patterns expressed between pure species and hybrids. Bone morphometry was not a good character for classifying all hybrids into individual taxonomic categories but was good for classifying pure strains. A model developed by discriminant function analysis worked well for striped bass and white bass and for their F1hybrids but it was not successful for F2hybrids and backcrosses. Thus, larval and juvenile hybrids of the Morone complex may be confused with sympatric pure-strain stocks even when identifications are based on interdigitation patterns or bone morphometry. This confusion may only further complicate management where stocking programs have been initiated to enhance or restore native stocks of striped bass and where hybrids have been introduced.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<719:PIPAMO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Striped bass Morone saxatilis were collected from mixed-stock populations in New Jersey, New York, Connecticut, Rhode Island, and Massachusetts coastal waters in spring and fall 1983–1986 for purposes of stock identification. Four morphometric characters and abundances of six eye lens proteins were used in a growth-invariant discriminant function analysis for classification into Hudson River stock or Chesapeake Bay-Roanoke River group. Correct classification rates were 76 and 80% for the Hudson River stock and the pooled Chesapeake Bay-Roanoke River group, respectively. The contribution of the Hudson River stock to the coastal populations varied between 14 and 89%, depending upon season and sampling location (state). Several factors influenced stock composition estimates, including year-class or size composition of the sample, geographical distribution of sample sites, sampling period duration, and season.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<728:GDACOS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Yearling coho salmon Oncorhynchus kisutch and steelhead Salmo gairdneri were exposed to high (2–3 g/L) or low (0.4–0.6 g/L) concentrations of three kinds of suspended solids (topsoil, kaolin clay, and volcanic ash) as long as 7–8 d. Such exposure did not cause mortality, but plasma cortisol concentrations were temporarily elevated in both species after exposure to 2–3 g/L of suspended topsoil, indicating that such exposure may have been stressful to the fish. Feeding rates of both species were reduced at high exposure concentrations. Exposure of yearling steelhead for 2 d to high or low concentrations of suspended topsoil, kaolin clay, or volcanic ash induced similar elevations of plasma cortisol levels, and, in groups exposed to high concentrations, blood hematocrits were increased. Osmoregulatory performance in fresh water and after transfer to 26‰ seawater was unaffected, and gill tissue appeared normal, after exposure to suspended solids. Exposure of yearling steelhead to high concentrations of suspended topsoil reduced the fishes' tolerance of subsequent infection by the bacterial pathogen Vibrio anguillarum. These results suggest that coho salmon and steelhead can survive exposure to high concentrations of suspended solids, but may undergo sublethal physiological stress that reduces their performance capacity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<737:PEOCSA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Pathological tissue changes elicited by an internal anchor tag in spot Leiostomus xanthurus and spotted seatrout Cynoscion nebulosus were evaluated histologically. Forty-five spot (32 tagged fish and 13 untagged controls) and 13 tagged spotted seatrout were sampled periodically from 4 h to 4 months posttagging. Early tissue changes (4 h-4 d posttagging) in both species were characterized by acute inflammation and irritation. Changes included hemorrhage, fibrin exudation, extravasation of leukocytes, epidermal hyperplasia and spongiosis, and necrosis in exposed myotomes. Tags were progressively encapsulated and sequestered by fibrogranulation tissue in a similar sequence in both species, commencing with deposition and organization of fibrin at the tag surface. This early fibrinous capsule (at day 2) was infiltrated by leukocytes and fibroblasts, and by day 4–7 it was thickened, highly cellular, and well vascularized. Deposition of collagen within the granulation tissue capsule increased progressively for at least 8 weeks. Complications of this process occurred frequently in tagged spot, whereas the incision in control spot receiving no tag healed quickly and without complications. Almost all tagged spot showed secondary mycotic and bacterial infections, and several spot exhibited gross peritonitis. Other frequently observed complications included dislocation of scales, damage to peritoneum and ovaries by tag penetration, and displacement of tags into swimbladder or intestine. Several spot appeared actively to expel the internal anchor tag. Severe pathological changes in tagged spot suggest that both mortality and tag expulsion may have contributed to the relatively low (0.2%) tag return rate observed during the past 8 years for this sciaenid. We have discontinued tagging spot with the internal anchor tag and do not recommend its use. However, complications in spotted seatrout were minor, and tag expulsion was not observed. We have observed an 8.8% tag return rate and continue to tag this sciaenid with the internal anchor tag.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<745:HOTIAT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Subspecific differences in spawning period and first-year growth of largemouth bass Micropterus salmoides were investigated by examination of otoliths from experimental populations established in research ponds in Illinois. Compared with Florida largemouth bass M. s. floridanus, northern largemouth bass M. s. salmoides were spawned earlier and grew larger (total length, weight) during the first growing season. Intergrade fish exhibited characteristics of age and growth intermediate between those of the two pure parental subspecies. The observed differences in size were independent of age, indicating that first-year differences in size were enhanced by genetic differences affecting growth rate. Peak production of F1intergrades occurred during the overlap in the northern and Florida largemouth bass spawning periods. However, F1intergrades were produced throughout the overall period of largemouth bass spawning.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<757:SPAFGO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The time required for a meal to be completely eliminated from the digestive tract of the lemon shark Negaprion brevirostris was determined X-radiographically, with barium sulfate as a contrast medium. Two food markers and X-radiography showed that initial voidance of fecal matter began 16–17 h after feeding. Alimentary tracts emptied completely within 68–82 h after food ingestion. Passage of a meal through the digestive tract took substantially longer than in most teleosts. A slow rate of food passage may contribute to the low consumption of food and slow growth that have been observed for the lemon shark.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<763:XOOFPT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The quantitative accuracy and effectiveness of a 1-m2benthic fish sampler was determined in riffles of three central Kentucky streams. The portable sampler is screened on three sides and has a collection bag on the downstream side; the top and bottom are open and, when in use, the sampler is placed directly on the substrate. Electrofishing and substrate disturbance within the sampler were used to dislodge fish into the collection bag. Electrofishing efficiency and sampler accuracy were estimated by subsequent application of a toxicant within the sampler and in blocknetted stream areas around it, respectively. In Kentucky streams, the mean efficiency of electrofishing within the sampler was 59% for fish collected in riffles, but efficiency was higher in spring and autumn than in other seasons. Kick-sampling was more effective than electrofishing in autumn and winter. Riffle fish population densities were estimated at an accuracy of approximately 63% when the sampler was used. For fish densities less than 6 fish/m2, over 200 samples may be needed to gain 95% confidence that the sample mean is within 10% of the population mean, but the minimum number of samples decreases rapidly as fish density or allowable statistical error increases. This sampler appears to be a useful and reliable device for obtaining quantitative samples of small benthic fishes in riffle habitats.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<768:BFSFUI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor