摘要:

The annual variation in sea‐age of maturation for a hatchery dependent stock of Atlantic salmon was compared to variation in post‐smolt growth as evidenced by circuli spacing patterns. The proportion of returns of 1‐seawinter (1 SW) and 2 SW salmon and the fraction of the smolt year class or cohort that maturated as 1 SW fish, were compared to seasonal growth indices determined from circuli spacing on the scales of smolt class survivors returning as 1 SW and 2 SW spawners. Using image processing techniques, we extracted inter‐circuli distances from scales from 2244 recaptured fish. Spacing data for the first year at sea were collected and then expressed as seasonal growth indices for the spring period, when post‐smolts first enter the ocean; the summer, when growth appears maximal; and winter, when growth appears to be at a minimum. In general, circuli spacings were wider for 1 SW than for the 2 SW returns of the same smolt cohort. The 1 SW fraction was significantly and positively correlated with late summer growth, suggesting that growth during this season is pivotal in determining the proportion of a smolt class that matu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01414.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The onset and development of cannibalistic behaviour were observed in early life stages of yellowtailSeriola quinqueradiata. Cannibalistic behaviour was divided into four actions, i.e aim, chase, nip and ingestion. The frequency of chase was used as an index of cannibalistic behaviour because it always appeared in every sequence of cannibalism, although a sequence of cannibalistic behaviour sometimes stopped before nip or ingestion. No cannibalistic behaviour was observed during the larval phase until day 22 after hatching (when fish were 9.6mm T.L.) either in a rearing pond or in experimental tanks. The onset of cannibalistic behaviour was observed on day 23, coinciding with metamorphosis from the larval to juvenile phase, and it developed until day 39, with a tentative decrease between day 33 and day 36. This inverted peak corresponded roughly to the development of schooling behaviour after day 33, which was determined by distance to the nearest neighbour. In the rearing pond, suffocation of a cannibal by its prey, appeared from day 23. Field observation of juvenile yellowtails aggregating around floating seaweeds showed that cannibalism occurred in three out of 10 schools, in which six cannibals were found among 194 fish. Cannibalistic behaviour in early life stages of yellowtail may occur as a final phase of inter‐individual interference and may have a role for size selection of a School membe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01415.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Formation of year‐class strength of breamAbramis brama, the most abundant fish in shallow eutrophic Lake Tjeukemeer, was studied during a 14‐year period. Although the size of the spawning stock of bream was rather stable during this period, analysis of length—frequency distributions indicates that it comprised only a few year‐classes. The strength of a year‐class was determined at a fork length of about 11 cm, at the end of the second summer. Mortality rates of fish larger than 11 cm were low (<50% year−1). As the number of fish at the end of the second summer was not correlated to the number of 0+ in the previous year, mortality rates during the second summer (ranging from 75.6 to 97.7% year−1) determine the final year‐class strength. These mortality rates were positively correlated to the year‐class strength of 2‐ to 4‐year‐old pikeperch. The abundance of this predator, therefore, is likely to be the most important factor controlling the year

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01416.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Swimming speed and activity costs of dace (Phoxinus eos × P. neogaeus) were estimated in the field using underwater video cameras. Activity costs were estimated by converting swimming speeds and the number of movements into swimming costs. Average swimming speed ranged from 6.7 to 12.2 cm.s−1across 2 h periods and varied significantly among dates and time of day. The time spent swimming by dace ranged from 616 to 17 640 s 2 h−1. Activity costs per 2h period ranged from 2.1 to 4O.2J 2h−1and were strongly correlated to the time spent swimming. Daily activity cost estimated using the cameras averaged 128.9J day−1and was equivalent to 1.7 times the standard metabolic rate. Activity cost predicted using a bioenergetic model in conjunction with independent estimates of consumption and growth rates averaged 138.8J day−1. This study indicated that swimming characteristics and activity costs of dace varied significantly both within and among days. These analyses also indicated that equally valid activity costs for fish in the field can be estimated using video cameras and the difference between Consumption and gr

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01417.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A purified mitochondrial DNA (mtDNA) probe was used to examine restriction fragment length polymorphisms produced by six restriction enzymes (XbaI,EcoRV,AvaII,HinfI, HaeIII,MboI) in 915 brown trout from western Europe. A total of 20 composite haplotypes were found with one to seven haplotypes in individual populations. Icelandic trout samples from north, south, east, and west coast drainages showed only a single common haplotype in contrast to the high level of polymorphism found in Irish and Scottish populations. The phylogeny of mtDNA haplotypes and the pattern of haplotype distribution suggests that post‐glacial colonization of brown trout in NW Europe was more complex than the dual colonization model which has been proposed on the basis of differentialLDH‐5*allele distribution. For example, Lough Melvin (Ireland) appears to have been independe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01418.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Smolt age and size, and individual growth during smoking were examined in a wild population of white‐spotted charr,Salvelinus leucomaenis, in a small stream in northern Japan. Smolt size (110–210 mm F.L.) differed neither between sexes nor among age cohorts of 2–7 years. Back‐calculation of riverine growth of smolts using otoliths showed a gradually increasing discrepancy in fork lengths of these age cohorts in both males and females, the faster‐growing individuals smolting at an earlier age. A mark—recapture study on individually‐identified fish revealed that the initial (spring‐summer) length‐frequency distribution of parr was unimodal, but became slightly skewed to the larger side in autumn, resulting in a bimodal distribution being evident by the following spring, with the upper modal group primarily composed of smolts. However, closer examination revealed that both male and female potential (subsequent) smolts were larger than the potential parr in the previous spring, the minimum lengths of the former being around 90–100 mm f.l. Specific growth rates of the potential smolts remained relatively high after summer through to the following spring, whereas those of the potential parr decreased after summer, despite having been similar between the two groups during the previous spring and summer. These observations revealed that the developmental triggering of smelting possibly occurs in or followin

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01419.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Female minnowsPhoxinus phoxinushave eight times as many club cells as males in their dorsal skin during the breeding season. The distribution of these cells is androgen sensitive and they may have an antipathogenic function. Since androgens also stimulate development of secondary sexual characters and depresses the immune system the putative role of nuptial coloration as a signal about immune function is discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01420.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

It can be predicted that common carpCyprinus carpio, as an introduced species, would harbour poor helminth infra‐communities but that these would nevertheless be richer than those in three other species of carps introduced into Europe in recent decades. These predictions were tested by comparing the helminth infra‐communities of common carp,Ctenopharyngodon idella, Hypophthalmichthys molitrixandAristichthys nobilisreared under similar conditions in a fish farm. Data were presented on species richness of total helminth infra‐communities, and on richness and diversity of gill, eye and intestinal infra‐communities separately. These confirmed that common carp helminth infra‐communities were poor and that they were no richer than those of the three other species of carp. This situation in the farm was considered to be representative of the situation in natural habitats in Europe. It is suggested that the poor infra‐communities in common carp reflect the facts that their helminth communities are composed mainly of specialists, that they are not readily susceptible to invasion by specialists of other fish hosts and that, as introduced species, they have not had sufficient time to acquire many generalist helminths from native species of fish. The difference in time between the introduction of common carp into Europe centuries ago and the introduction of the other three species of carps decades ago is not sufficient to produce any significant differences in the richness and diversity of their helminth infra

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01421.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The eggs of only 13 macrourid species have been reported hitherto, eight identified from free buoyant eggs and five from ripening oocytes. Eggs of 11 species had raised, hexagonally patterned ornamentation on the envelope, while two species bore only partial ornamentation. Ripening oocytes of a further eight species showed that, overall, the eggs of 13 species had characteristic hexagonal ornamentation and three partial ornamentation, but four were smooth. Fertilized eggs ofCoryphaenoides (Coryphaenoides) rupestriswere found with smooth envelopes, while ornamented eggs have been reported for this species also. Little taxonomic significance could be attached to these results. Some correlation was found between the three categories of egg envelope ornamentation and species' bathymetric distributions. A recent model of egg development in a slope dwelling trachichthyid species suggested analagous potential ecological advantage for ornamentational variation in macrourids.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01422.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Growth and survival ofCyprinodon variegatus, Fundulus heteroclitus, Menidia beryllina, andLucania parva, held in combination with an omnivorous grass shrimp–Palaemonetes pugio, and a predatory diving beetleTropisternus lateralis, were measured at 12–60% in outdoor static microcosms that simulate salt marsh ponds. We predicted that the low species richness of this abiotically harsh but highly productive habitat would lead to a high degree of interaction among species. The presence of the beetle had no effect on the fish or the shrimp. Removal of the shrimp similarly had no detectable effect on the fish. There was a trend in proportions of survival among three fish:C. variegatus>F. heteroclitus>M. beryllina. Survival ofM. beryllinawas greater when it was alone at low densities of its own species (333 v. 667 fish m−3), and less when it was paired with F.heteroclitus. Interactions with other species diminished the growth ofM. beryllina. Survival of F.heteroclituswas greater when it was alone at low density (333 m−3), than when the same number were placed together withMenidiaandCyprinodonat a total fish density of 999 m−3. There were no effects of removal of other species on survival or growth ofC. variegatusat either 12′5 or 24%. This study showed that a complex array of interactions occurred among six common members of a salt marsh food web, but the degree of interaction Was less than W

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01423.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY