摘要:

Migratory behaviour at spawning of wild and newly‐escaped farmed Atlantic salmon was analysed by radio telemetry in the River Alta, North Norway. Spawning areas were located by aerial surveys. Farmed females moved significantly more than wild females (P<0.01). There was no such difference between the two groups of males. About 83% of the wild fish stayed within identified spawning areas for 1 day or longer. The corresponding figure for farmed salmon was only 43% (P<0.05). Wild salmon stayed 8.1 days inside spawning areas and farmed salmon 5.2 days. The present results suggest that escaped farmed salmon had reduced spawning success compared with wild fis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05942.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Demersal fish were sampled over 3 years to describe sealwormPseudoterranova decipiensinfection levels in relation to the size of a local colony of common sealsPhoca vitulinain Hvaler, Oslofjord, Norway. More than 2000 fish were examined for worms, and five fish species were found to be infected, codGadus morhua, four‐bearded rocklingEnchelyopus cimbrius, plaicePleuronectes platessa, long rough dabHippoglossoides platessoidesand dabLimanda limanda.A detailed analysis of worm accumulation in cod, the only infected species present in large enough numbers, shows a net decrease in worm transmission following the phocine distemper virus epizootic which killed two‐thirds of the seals in Hvaler in 1

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05943.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Infections with metacercariae ofBucephaloides gracilescensin the four‐bearded rocklingEnchelyopus cimbriuswere studied for a year in a Norwegian fjord. The prevalence was at all times high, but abundance showed a marked decline in spring to a low level during summer. A rise in abundance, variance‐to‐mean ratio and frequency of smaller metacercariae in early autumn (August‐September) shows infection to have occurred mainly in autumn. There were no differences in level of infection between host sexes, but a highly significant positive correlation of parasite burden with host length. No influence on the condition factor of the host was revealed, the parasite cysts in the central nervous system are believed to have low pathogenicity. A detailed account of the distribution of metacercarial cysts is given. No support for infection being via the lateral line canals is revealed, cercarial penetration is believed to be through the general surface of the head and through the unpaired fins of the trunk a

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05944.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The size and composition of finfish yield from six Fijian reef fisheries was determined using catch records from a voluntary logbook scheme. A total of 172 logbooks were issued for 30‐day periods in October 1992 and February and June 1993 and they provided information on 1369 fishing trips. Catch records were weighted, using the results of contemporaneous fishing activity and fleet size surveys, to provide yield estimates for each fishing ground (qoliqoli). Yield from allqoliqoliwas dominated by Serranidae and Lethrinidae which were favoured for consumption and sale. Yields were expressed on the basis of reef area for fish from different trophic groups. Macroinvertebrate‐feeders and piscivores accounted for more than half the yield in allqoliqoliand there were significant differences in area specific yield betweenqoliqoli.There was no evidence of fishers adopting more powerful fishing techniques or catching fish from lower trophic levels in order to maintain yield from anyqoliqoli.This suggested that the fisheries examined were all capable of sustaining the reported yields of up to 3.4 tonne km−2qoliqoliyear−1or 10.2 tonne km−2coral reef year−1and that in sites where yields were less they might be increased

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05945.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Smelt, flounder, eel, three‐spined stickleback, twaite shad, ruffe and herring were the major species among 62 forming the fish community of the Elbe estuary. Species richness, species diversity, evenness and total fish biomass decreased in the upstream direction. Total abundance was greatest during summer. Salinity was the most significant physico‐chemical factor affecting species richness and total fish biomass, whereas water temperature was the best predictor of total abundance. Marine fish species decreased with decreasing salinity, while the freshwater species roach and ide were absent at salinities>15‰. Bream, blue bream, white bream, perch and pikeperch occurred more frequently in shallow marginal regions with lower current velocities, while herring and other marine species occurred closer to the deep central regions with high current velocities. Annual and seasonal variations of the community structure mainly reflected in population dynamics of smelt, flounder, twaite shad, three‐spined stickleback and eel, especially those of 0‐age smelt. Populations of smelt and ruffe and their importance in the fish community increased between 1989 and 1992, while those of twaite shad and eel decreased. At oxygen concentrations<3 mg I1, smelt and flounder were rare, but eels were at their maximum at 3.5 mg I−1. Changes of species composition and fish abundance were closely related to daytime and

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05946.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

One‐ and two‐year‐old hatchery reared juveniles of seven freshwater resident and anadromous populations of Scandinavian brown trout were released in the outer and inner part of the Oslofjord and in the River Akerselva, flowing through the city of Oslo. Recapture rates were highest (mean 20.3%) for river released fish and lowest for those released in the outer (16.8%) and inner (12.1%) fjord. In general, recapture rate increased with fish size at release (r=0.76). When released in fresh water, most of the recaptures were from fresh water and when released in the fjord, most recaptures were from the fjord. In general, freshwater resident stocks showed a higher degree of freshwater residency than anadromous stocks. However, mean migratory distance was longer for freshwater resident than anadromous fish. Trout moved longer distances at sea when released in the outer than in the inner fjord. Specific growth rate and size at recapture varied among release sites and stocks; they were highest for fish released in the outer fjord and lowest for river‐released trout. There was no consistent difference in sea growth between freshwater resident and anadromous stocks. Estimated total yield was highest for fish released in the outer fjord, whereas there was no significant difference in yields between trout released in the river and the inner Os

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05947.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The appearance of deformed vertebrae from a single mature female school shark,Galeorhinus galeus, are described. Two unusual, pronounced bumps were noticed in the caudal region of this shark. There were no scars in the skin over these protrusions, suggesting that the lesions had arisen internally. Radiographie and histologie investigation of these lesions showed that mineralized tissue had probably been lost following an injury to the tail. Histological observations provided circumstantial evidence that mineralized tissue had been removed by internal processes, but did not reveal the agency by which skeletal tissue had been resorbed. Since the capacity to resorb mineralized tissue is characteristic of animals possessing bone, the apparent loss of mineralized tissue seen in this shark provides circumstantial evidence for the existence of bone cell lineages in school sharks. This evidence is discussed in relation to the possible implications for evolutionary and fisheries biology.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05948.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Survival, biomass and diet of pike,Esox lucius, larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m−2in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mmt.l.) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mmt.l.). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha−1) and 121 mm T.L. (181.8 kg ha−1) and stabilized between 121 and 139 mmt.l. Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mmt.l.) and between 74 and 121 mmt.l. (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mmt.l. juveniles. Average‐sized pike exhibited a sequence of size‐dependent shifts from a diet composed primarily (in terms of weight) of micro‐crustaceans (at 13 mmt.l.), to chironomid larvae (at 74 to 99 mmt.l.), and finally macrocrustaceans (at 121 to 139 mmt.l.). Cannibalism was detected first among the largest fish at the 74 mmt.l. stage. Between‐year diet similarity at various developmental stages was consistently high. In 70 mmt.l. fish harvested from different ponds, we found significant among‐pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquacu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05949.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Changes in electroencephalogams (EEG) and cerebral blood flow were examined in carp immobilized with a muscle relaxant during 60 min hypoxia (waterPo2of approximately 20 mmHg) and subsequent 30 min normoxia. The amplitude of EEG waves recorded from the telencephalon decreased gradually but slightly with the progression of hypoxia, whereas the telencephalic blood flow increased mainly due to an increased blood velocity. These findings suggested that cerebral activity during hypoxia was compensated to some degree by increased cerebral blood flow. However, carp showed large variations in the patterns of EEG responses and cerebral blood flow.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05950.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Oxygen consumption (V̇o2) and respiratory variables were measured in the Prochilodontid fish,Prochilodus scrofaexposed to graded hypoxia after changes in temperature. The measurements were performed on fish acclimated to 25°C and in four further groups also acclimated to 25°C and then changed to 15, 20, 30 and 35°C. An increase in V̇o2occurred with rising temperature, but at each temperature V̇o2was kept constant over a wide range of O2tensions of inspired water (Pio2). The critical oxygen tensions (Pco2) werePio2= 22 mmHg for 25°C acclimated specimens and after transfer from 25°C to 15, 20, 30 and 35°C thePco2changed toPio2= 28, 22, 24 and 45 mmHg, respectively. Gill ventilation (V̇G) increased or decreased following the changes in V̇o2as the temperature changed and was the result of an accentuated increase in breath frequency. During hypoxia the increases in V̇Gwere characterized by larger increases in breath volume. Oxygen extraction was kept almost constant at about 63% regardless of temperature and ambient oxygen tensions in normoxia and moderate hypoxia (Po2∼70 mmHg).P. scrofashowed high tolerance to hypoxia after abrupt changes in temperature although its survival upon transfer to 35°C could become limited by the capacity of ventilatory mechanisms to alleviate

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb05951.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY