摘要:

The effects of an episodic event, involving the cyclonic flushing of, and associated rapid decrease in salinity in an estuarine system, on two faunal components was investigated. The rapid salinity decrease of some 25% had a direct, short‐term effect on most components of the benthos of Lake St Lucia, as well as a long‐term effect on the bivalves, particularlySolon cylindraceus, which species was unable to re‐establish itself at previous densities. Indirect long‐term effects were noted in the diet ofSolea bleekeri, which feeds predominantly on the siphon tips of S.cylindraceus, in that it switched to feeding on whatever prey it could locate at the surface of the benthos. Although no change in densities ofS. bleekeriwas noted after the event, it is considered that the resultant change of diet did lead to some stress in the population. This study clearly demonstrates the need to monitor episodic events due to the direct and indirect effects, either short‐ or long‐term, which they may have on the estu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05552.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Ambassidae are represented in South African estuaries by three species which are very similar in external morphology, feeding ecology, alimentary system and distribution. The co‐existence and spatial separation of these species ofAmbassisin the estuaries of southern Africa can be explained by the tolerance of each to salinity and temperature. Investigations of the temperature tolerance ranges of the three species suggest that the osmoregulatory capability ofAmbassis productusin reduced salinities (25% (estuary mouths) andA. natalensisto intermediate salinities associated with the middle reaches of estuar

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05553.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

During their first 6 months sibling Atlantic salmon parr,Salmo salarL., grew larger under constant light than under natural photoperiod or simulated natural photoperiod (control). When rate of change of photoperiod was accelerated after midsummer, ×2, ×3 and ×4, there were no growth differences between the three groups, but all were smaller than the control population. Under constant autumn photoperiod of 8 h light: 16 h dark growth was less than under all other experimental photoperiod conditions. Mean length was directly correlated with total hours of daylight experienced, excluding those fish kept under constant light.Fish reared from first feeding under photoperiod regimes delayed 6 and 9 months out of phase with the natural light cycle were smaller than the controls, whereas those under a regime 3 months out of phase did not differ from the controls. The clear segregation of modal length groups within the 3, 6 and 9 months out‐of‐phase populations occurred 1, 4 and 4 months, respectively, after the segregation in the control group. Under constant light, and under constant 12 h light: 12 h dark (12 LD), the segregation was delayed 3 and 4 months, respectively. The proportion of the population which maintained growth (upper modal group) was significantly less in the 9 and 6 months out‐of‐phase and 12 LD groups (39, 40 and 42%, respectively) than in the other three groups (82.5‐85%). Acceleration of photoperiod change also resulted in decreased growth.The results support a model of salmon development in which, 2‐3 months after first feeding, growth is maintained if feeding opportunities at that time are above a threshold level, and in which this critical timing is influenced by photoperiod. It is suggested that the delays reflect a synchronizing effect of photoperiod on an endogenous rhythm of appetite and growth. The differences in upper modal group proportions observed in the present experiments, reflect the relative feeding opportunities available at the critical period

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05445.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

With the aid of models and selected examples, an analysis of speciation within the family Atherinidae is presented. This is a large family of pelagic fish, many members of which look strikingly similar. They are primarily a marine coastal group, favouring sheltered estuaries and lagoons, although in some regions they have invaded fresh waters.Many atherinids show a high degree of intraspecific morphological variability which can be linked to their estuarine habitat. It is argued that estuarine and lagoonal environments are physically highly variable and this has acted to select for generalist genotypes able to adjust their morphology, physiology and behaviour to a wide range of conditions. Such plasticity pre‐adapts atherinids to invade and rapidly speciate in fresh waters containing vacant niches. Examples of such invasions and speciation are presented, and the rate of evolution discussed.The selective forces acting on atherinids should be common to other fish groups, suggesting that many freshwater fish may have estuarine ancestors. The influence of estuaries in evolution may be out of all proportion to their siz

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05554.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Information on estuary‐dependence of bass in U.K. waters is summarized from recent published reports and some unpublished data.There is substantial reliance on estuaries (including tidal backwaters with little freshwater inflow) such as the Hampshire harbours, in the first 4–5 years of life. Man‐related hazards to survival are considerable and increasing: they include destruction of or damage to habitats, losses of 0‐groups in power‐station intakes, and excessive unregulated fishing effort, mainly on 4–5‐year‐old bass. Some measures to protect bass in estuaries are now in hand, but much rem

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05555.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Two distinct site‐specific populations ofDiploslomumspp., occurring concurrently in the lens and retina of naturally infected rainbow trout, were different morphologically. They represent separate populations epidemiologically. The lens and retina metacercariae did not differ immunologically when tested by an enzyme‐linked immunosorbent assay against immune rabbit and trout antisera. Antibody titres became positive by September 1982 in a natural population of yearling rainbow trout infected with lens and retina metacercariae and remained positive for at least 8 months. The antibodies formed may offer protection against reinfections withDiplostomumspp. cercar

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05446.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

128 fish species were recorded for the mangroves of Pagbilao. Aspects of the population dynamics of the common species,Ambassis kopsi, Secutor ruconius. Leiognathus brevirostrisandProsopodasys gogorzaewere investigated. Growth coefficients varied from 0.41 to 1.2. Mortality in the mangroves was high, and most species there breed once per year.Species diversity (H') of the community ranged from 1.05 to 2.9. It was influenced by evenness rather than by species richness. Species abundance gave a log normal distribution, except during the typhoon, when it fitted the niche preemption model.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05556.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The common goby,Pomatoschistus microps, is an abundant brackish water species which has an appreciable role, both as predator and prey, in the ecosystems of British estuaries. The partitioning of energy within each sex is described and discussed, and energy values are provided for the gonad, liver and carcass throughout almost the entire life of one year class. Partitioning of resources within the body at different times of the year shows considerable variation, not only with time but also between the sexes. In particular, the energy content of the male gonad during the spawning season is never more than 3.7% of that of the female. Important aspects of the biology of the species which relate to energy partitioning are maturation at an early age, high reproductive investment, high stochastic mortality, and death usually after a single breeding season.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05557.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The environmental quality objective and standards (EQO/EQS) approach to controlling and assessing estuarine pollution is described together with details of the information necessary to assess the health of the fish populations and determine whether the EQO/EQS are being met in an estuary. These concepts are illustrated by examples from the Forth estuary, Scotland, involving studies of the ecology, pathology, biochemistry and contaminant bioaccumulation of fish in relation to the benthos, water quality and anthropogenic influences.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05558.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The distribution and growth of roach and dace in the R. Exe catchment was studied. Distribution conformed to the classic theories of zonation, although human interference extended or reduced the range of species. Distinct differences were found in the growth rates of roach and dace between different regions of the catchment. Both species achieved their fastest growth in zones where the river topography portrayed their ‘preferred’ habitat characteristics, i.e. the fast‐flowing middle and slow‐flowing lower reaches for dace and roach, respectively. Female roach were found to grow considerably faster than male fish, whilst no sexual differentiation in growth rates was found in dace. Considerable fluctuations in year class strength were observed in both

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05448.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY