摘要:

Gut evacuation and absorption efficiency in zooplanktivorous walleyeStizostedion vitreumlarvae (10–19 mm; 0.53–6.8 mg dry weight) were examined in the laboratory. The decline in dry weight of whole digestive tract contents was examined at 15, 20, and 25) C in discontinuous feeding larvae. The observed relationship between short‐term evacuation rate and gut fullness indicated that evacuation approximated most closely an exponential decline. When gut evacuation rate,R, was calculated as the slope of loge gut fullnessv. time there were significant effects of temperature and walleye size onR. Gut evacuation rate was higher at 20° C than at 15 or 25° C and declined with increasing walleye dry weight. Absorption efficiency at 20° C was examined by qualitative analysis of food and faeces. Apparent digestibility,Da, of crustacean zooplankton increased with gut retention time and declined with walleye dry weight. MaximumDawas estimated to be 79% of organic matter from food retained in the gut

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00035.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Juvenile plaice,Pleuronectes platessa(n=6, 151–197 mm SL) and dabLimanda limanda(n=6, 119–180.5 mm SL) feeding on pieces of mussel flesh were studied by high‐speed (200 fields s−1) videophotography at 11) C. Prey capture cycles (involving jaw protrusion and opercular expansion) were described in both species. The capture cycle was followed by at least one cycle (similar to the capture cycle in all respects except food intake) which is believed to transport food to the oesophagus. The transport cycle (or cycles) was followed by a species‐specific number of normal respiratory cycles (7 or 8 in plaice, 11 or 12 in dab) and a final single cycle when food debris was violently ejected from the opercular cavity. The respiratory cycles and ejection cycle cleansed the orobranchial/opercular cavities and gills. Differences between the species were relatively minor, but plaice captured and transported food more quickly

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Prevalence and abundance ofGyrodactylussp. on the 1993 year‐class of sand gobiesPomatoschistus minutusin the Oslo Fjord, Norway, decreased slightly during the cold months, increased as temperature increased in spring, reaching a peak in June, then decreased significantly, corresponding with a decline in the number of hosts from August. Abundance and, especially, prevalence increased again in September, and decreased in late autumn. Death of the most heavily infected hosts, and/or host resistance might be responsible for the decline in parasite numbers on post‐spawners in summer. The young of the year (1994 year‐class) were probably infected shortly after they commenced benthic life in July, and prevalence and abundance increased significantly throughout late summer and autumn. Parasite abundance on males was significantly higher than on females at the height of the breeding season in June, but significantly lower at the end of the breeding season in July. Two‐thirds of the parasites infected the gills, oral cavity and pharynx. The proportion of parasites on the body, head and fins increased on both sexes, but significantly more so on males, during the breeding season of the host, when parasite intensity was highest. Possible routes of transmission of the parasite are di

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Geographic variation in minisatellite DNA variation was examined in 18 stocks of coho salmonOncorhynchus kisutchfrom British Columbia and three stocks from Kamchatka or Western Alaska. Genomic DNA was restricted withMboI orHaeIII and hybridized with two minisatellite probes (pSsa‐A34,OtsPBS‐1). Allele frequencies and DNA band counts derived from the two probes were combined with band counts from the probeSsato show a regional stock structure. In British Columbia, stocks from the Fraser River were distinct from those on Vancouver Island, and all were differentiated from those on the mainland of British Columbia. Average heterozygosity at theSsa‐A34 locus was 71%. Compared with a previous study of British Columbia coho salmon population structure in which variation at 26 allozyme loci was examined, greater population differentiation and higher heterozygosity were observed at minisatellite loci. Estimated stock compositions of simulated mixtures of fishery samples from British Columbia stocks were accurate and precise, with the potential of identifying stocks within the drainage basin of a major river, the Fraser River. Minisatellite DNA variation may provide accurate and precise estimates of stock composition in actual fishery applications, and has the potential of identifying individual fish to region or stock of o

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Exposure of embryos ofChondrostoma nasusto a strongly reduced oxygen content (about 10% of air saturation) enhanced mortality and depressed hatching success. Viable larvae hatched only from the controls and from the group exposed to reduced oxygen during the earliest embryogenesis (from fertilization to gastrula). In the groups exposed from gastrula to eyed stage and from eyed stage to hatching, a high percentage of fish hatched, but all were deformed and almost all died during the following 1–5 days. Hatching period was prolonged in the groups exposed to reduced oxygen content. At a spawning areaC. nasushad deposited a large portion of eggs in areas of reduced oxygen content. On the other hand, eggs placed at the substratum surface were exposed to high predation pressure fromBarbus barbus, Lota lotaand ducks (Anas platyrhynchos). The trade‐off between predation pressure at the substratum surface and reduced oxygen conditions in the interstices resulted in a narrow space for successful development of embryos of this endangered rheophilic fish species under natural conditi

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The perch foraging pattern in a Finnish lake (64) N) was crepuscular and they moved into littoral areas at dusk and returned to deeper waters by dawn. Predation on vendace larvae was guided by environmental cues, mainly temperature and light periodicity, which affected the density and foraging activity of perch in the littoral area. The availability and the vulnerability of different food categories were both responsible for the perch diet. The hypothesis that perch have a generally decisive role in the regulation of vendace larval abundance through predation at the time of high vendace larvae concentration in the littoral area was not supported. We emphasize the need to evaluate biological phenomena, such as predator–prey relationships, in the light of the relevant physical variables, and to do so within appropriate time and space scales, instead of relying on indirect estimates of the predator and prey population abundance and using their reciprocity as evidence of the interactio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Testicular ultrastructure was studied inBarbus longiceps, Capoeta damascinaand their natural hybrid. The testes of these teleosts belong to the unrestricted or lobular type. Germ cell morphology is similar in the parental males. In the hybrid, spermatogenesis does not extend beyond the pachytene of the first meiotic division, probably due to the unsuccessful pairing of the homologous chromosomes. Hybrid testes are occupied mainly by degenerating primary spermatocytes, at the leptotene and pachytene stages. In both parents and the hybrid, Sertoli and Leydig cells are characterized by the presence of granular endoplasmic reticulum and of mitochondria with tubular cristae. Due to the arrest of spermatogenesis, the male germ cell protective barrier is absent in the hybrid. Germ cell nuclear size was measured by a computerized analysis system, using light‐microscopy images. In the parents and the hybrid, germ cells attain a uniform inter‐individual nuclear size when they reach the first meiotic prophase. The nuclear size of primary spermatocytes is similar among the three groups of fish, possibly reflecting their close genetic relations

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Previously biomass predictions have been derived from simple weight—length relationships. This study measured a variety of truss and conventional dimensions covering the lateral body profile of Atlantic salmonSalmo salarand, using regression analysis, developed a series of multifactor weight—lateral dimension relationships. Single‐factor regression equations proved inadequate for predicting weight with percentage errors between real and estimated values ranging from −1.2±6.8% to 72.5 ± 225.6%. Fifty‐two multifactor regression equations were generated that predicted accurately the weight of individual fish to within ±2% using combinations of conventional and truss measurements. Regression coefficients were found to be significantly different (P<0.05) between Scottish and Norwegian strains, indicating morphological differences between the genetic groups. Norwegian fish were generally heavier for a given length compared to Scottish strains. This suggests that morphologically different strains ofS. salarwould require individual weight: lateral dimension relationships to be developed in order to predict biomass accurately to within commercially accep

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

This paper describes the results of a study of the effects ofSchistocephalus soliduson one of its intermediate hosts, the sticklebackGasterosteus aculeatus, in an annual population in which infection is known to occur in one major wave in autumn. Weight, as a function of length, was lower in infected sticklebacks compared with uninfected fish during autumn and spring; in winter and summer, both categories of fish were in equally poor condition. In early autumn, the hepatosomatic indices of newly infected fish were higher than those of uninfected fish, perhaps due to a pathological response. Thereafter, relative liver size of uninfected and infected sticklebacks was comparable until spring, when it increased sharply in uninfected sticklebacks but remained stable at a low level in infected sticklebacks. Few infected fish reached maturity. The only males to attain maturity whilst sustaining an infection ofS. soliduswere in particularly good condition. Nuptial coloration, kidney hypertrophy and testes size were unimpaired in these mature infected males, but whether they were capable of successful reproduction remains debatable.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Responses to environmental heterogeneity were studied in laboratory‐reared offspring of two morphs of Arctic charrSalvelinus alpinusfrom Loch Rannoch, Scotland, one occupying the pelagic zone and feeding predominantly on zooplankton and the other being benthic in habit and feeding mainly on macroinvertebrates. When housed in groups in tanks with a black‐and white striped base, benthic charr demonstrated a clear preference for dark areas, whereas pelagic fish positioned themselves at random with respect to substratum colour. In general, pelagic charr were much less aggressive than benthic charr. In pelagic fish, neither spacing nor aggression was affected by the visual heterogeneity of the substrate. In contrast, benthic charr swam closer together and fought more when housed over a uniform as opposed to a non‐uniform substratum. The results are discussed in the context of habitat‐specific visual requirements and of an interaction between visual complexity and territoriality previously described for Atlantic salmonSalm

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY