摘要:

The fish population of a flat marine area (near Imperia in the Ligurian Sea), depths between 4 and 8 m, colonized by the allochthonous algaCaulerpa taxifolia(Valhl) C. Agardh, was studied during a series of observations from October 1994 to October 1996. Visual censuses and catches using 200 m trammel nets were carried out. Fifty different fish species were observed, Sparidae and Labridae, with 12 and 10 species respectively, were the two most represented families. Maximum Shannon‐Weaver index obtained by censuses was 3.29 and by net catch 3.40. Abundances ofSymphodus tineaandScorpaena porcusseemed to be a characteristic of this community. A comparison with fishing data obtained in a control area withoutC. taxifolia, but colonized by the phanerogamCymodocea nodosa, gave an idea of the changes produced in the fish population as a consequence of the spread of the allochthonous alga. A comparison with Mediterranean rocky environments indicated the existence of some shared qualitative characteristics as well as lower fish densities on theCaulerpaat the Imperia site.

ISSN:1125-0003    

DOI:10.1080/11250009809386867

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Predicted global warming is expected to raise the water temperatures 2–6° C after doubling of atmospheric CO2. As an extreme coldwater fish species the Arctic charr appear to avoid water temperatures above 16–18° C. Arctic charr lives in Finland only in the mountain lakes of northernmost parts of the country and in some deep lakes of eastern Finland. Charr is most abundant at high altitudes. The global warming is expected to threaten first populations living in low altitude shallow lakes in which no thermal summer stratification occurs. Climatic warming will increase duration of high temperatures and thermal stratification in deep lakes. This indicates that Arctic charr will spend longer periods in minimum thermal habitats. Assuming that no factors other than temperature will change in future climates, reductions in summer habitat will probably lead to noticeable reductions in many charr populations. Populations living in deep lakes will survive better than those living in shallow lakes provided that the water quality of these lakes does not deteriorate.

ISSN:1125-0003    

DOI:10.1080/11250009809386868

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Rainbow trout embryos(Oncorhynchus mykiss)in different development stages were exposed to the influence of a constant magnetic field (5 and 10 mT). An increased oxygen uptake was observed in embryos influenced by the field activity as compared to those which develop in a geomagnetic field. The effect of a magnetic field on the breathing processes of embryos was more pronounced in the periods of an advanced morphogenesis.

ISSN:1125-0003    

DOI:10.1080/11250009809386869

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Constant magnetic field of low value slows down the embryonic development of trout(Salmo trutta), rainbow trout (Oncorhynchus mykiss).Hatchlings were longer and heavier, and also more motile than those in the control experiment. Magnetic field induces a change in the circulation motion in embryos and larvae of pike(Esox lucius)and carp(Cyprinus carpio), and in the embryos of trout (5.tnitta).Exposure to magnetic field in embryos causes an increase in a heart rhythm, particularly during the early pulsation period of the forming heart. Magnetic fields cause a change in the gas exchange in embryos of a rainbow trout (O.mykiss).Intensity of breathing processes increase in a magnetic field, however, is dependent on stage of embryonic development, and it is especially manifested in the period of an advanced organogenesis. Embryos of rainbow trout (O.mykiss)and trout(S. tnttta)exhibit a sense of direction both in natural and artificially created magnetic field.

ISSN:1125-0003    

DOI:10.1080/11250009809386870

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The objectives of this study were to determine the effects of acidification on 0+juvenile fish diversity and abundance in River Kyrönjoki in 1995 and 1996. Species diversity and abundance data were obtained from seine hauls in aquatic vegetation biotopes of nymphaeids predominantlyNuphar lutea.Acidity levels decreased steadily from May to August in 1995. In 1996, acidity levels increased during May, July and early August. Acidification levels were related to low abundances of 0+juveniles, except for 0+juvenile(Esox Incites L.)in the estuary, and lower species richness in the 0+fish community in the river in 1996. Single species dominance, expressed as rank abundance curves, was typical in the river's 0+juvenile fish community during the acidification in 1996.

ISSN:1125-0003    

DOI:10.1080/11250009809386871

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Compost manure contains humic acid which can chelate metals in water and reduce toxicity and bioavialability. Static (180 day) bioassays were made in outdoor cement tanks (300 liters) with air breathing fishHeteropneustes fossilisexposed to 2.5 mgliter‐1cadmium (Cd) treated individuallly and with three different levels of compost manure made from fresh water macrophytePistia stratiotes.Addition of compost manure significantly reduced the concentrations of dissolved Cd in water and whole body Cd in fish and plankton. For quick removal of Cd from water a high dose of the manure (6.7 guter‐1) was found more effective than a moderate dose (1.0 g‐liter‐1) or cumulative treatment at moderate dose (1.0 gliter‐1month‐1). The cumulative treatment appeared more effective in reducing whole body concentrations of Cd when exposure was continued for a long period. Growth of fish, in respect of length, weight, and yield were reduced by Cd exposure. Addition of compost manure reduced the ill effects on growth to fish produced by Cd. The high dose of manure immediately resulted a superfluous increase in dissolved inorganic nutrients (NO3‐N, NO2‐N, NH3‐N, PO4‐P) and primary productivity. Water quality remained within optimum levels recommended for most aquaculture practices when the manure was added at a moderate dose (either once or every month). However,H. fossiliscould tolerate water highly enriched in dissolved inorganic nutrients. Compost manure proved to be a promising tool to counter Cd toxicity in aquaculture, but to avoid organic enrichment a proper dose should be determined according to the condition available.

ISSN:1125-0003    

DOI:10.1080/11250009809386872

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Studies of actual ichtyological biodiversity in the European Atlantic Ocean and estimation of changes in the relative abundance of fish species in catches off Arcachon, on the shelf and in the Bassin d'Arcachon, from 1727 to the present day are made. These show that some previously dominant species are now rare. Several disappeared to the south of the Bay of Biscay, such as the bottom‐living elasmobranchs with low reproduction rates(Echinorhinus brucus, Squatina squatina, Raja batis, R. brachyura, R. clavata, Dasyatis pastinaca, Myliobatis aquila, Galeorhinus galeus, Mustelus asterias), and teleostean fishesTrigla lyraandEutrigla gurnardus.Overfishing with most fishing gears, but especially bottom trawls is responsible for their reduction. An additional study was made on tropical species which were not recorded before 1950 to the north of Portugal. The species includeZenopsis conchifer, Cyttopsis roseus, Chaunaxspp.,Sphoeroides pacbygaster. Tarpon atlanticus, Seriola rivoliana, S. dumerili, S. carpenteri, Lichia amia, Pomatomus saltator, Aluterus monoceros, Pisodonophis semicinctus, Lamprogrammus niger.Northward extensions in the distribution in Euro‐Atlantic sea waters of tropical fish are compared with results obtained in other regions of the South French Atlantic continental shelf. Ichthyological observations support previous results: 68.3% of the new records were fished on upper slope (200 to600m); 19.5% from the continental shelf (0 to 200 m). Among them, some 66.7% of captures from the south of the Bay of Biscay; 12.2% of the new records were found in the middle slope (900 to 1100 m). These results confirm the following: (1) a northern extension of tropical fishes on the upper slope in the south of Portugal has increased since 1963, and while it began in 1969 on the continental shelf, only increased from 1981; (2) the rate of colonisation of new‐comers was low for several species. About 30 years have passed between the record ofZenopsis conchiferand that ofCyttopsis roseusfrom off Portugal and northwestern Ireland, but only 5 years in the case ofSphoeroides pacbygaster, and (3) the northward expansion is evident to 52°00'N for continental shelf species, to 55°30'N for upper slope, and to 60°00'N for mid‐slope species.

ISSN:1125-0003    

DOI:10.1080/11250009809386873

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Most activities directed toward the conservation of freshwater fish biodiversity have focused on eliminating pollution and habitat degradation. However, according to decision making theory, every successful strategy has to be based on two components: elimination of threats; and amplification of opportunities. The question is, “What are the opportunities in conservation of freshwater fish and their habitats? According to the concept of the new UNESCO IHP‐V programme, ‘Eco‐hydrology’ is the integration of knowledge on the biota dynamics with the whole range of hydro‐logical processes; including the river system, catchment level, and microhabitat. Inclusion of the Eco‐hydrology concept will lead to a better understanding of the hierarchy of regulating factors and evolutionary established resistance/resilience of the freshwater ecosystem to stress. It implementation is especially important for efficient conservation because ecosystem managers have often limited their view to the single causes and simple solutions. To successfully change from a conceptual to an operational stage of the ‘Eco‐hydrology Paradigm’ there needs to be additional research on the dependence of fish life history and physiological performance on hydrological processes. This is chiefly because fish are regulators of processes in whole trophic cascade in aquatic ecosystems.

ISSN:1125-0003    

DOI:10.1080/11250009809386874

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Stizostedion luciopercareared in a recirculating water system were fed with natural (live zooplankton) and artificial food (trout granules). Fish fed different diets differed significantly in their growth, condition factor and survival (P < 0.05). At the end of the rearing period the level of proteins and lipids in the fish fed an artificial diet were almost 1% and above 5% higher than in fish fed Zooplankton. Amino acid composition of the fish was stable throughout the rearing period.

ISSN:1125-0003    

DOI:10.1080/11250009809386875

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Until 1996, scientific information about groundfish assemblages on southern Adriatic trawlable bottoms almost exclusively referred to the western side of the same basin (Italian waters). During 1996, for the first time, a summer trawl survey was carried out along the full South Adriatic area. A total of 93 demersal fish species was obtained and the ‘species abundance (biomass)/sam‐pling stations’ matrix was analysed by means of cluster analysis. The analysis was useful to discriminate the shelf and slope assemblages on both sides of the South Adriatic and to compare biodiversity. This was determined with univariate ecological indices (diversity, equitability) and graphical methods (ordinary, cumulative, and partial dominance; abundance/biomass comparison curves). Fish assemblage biodiversity was higher on shelf bottoms of the eastern Adriatic side (Albanian waters) than the western shore (Italian waters). The highest catch yields, referring to the main “target”; trawl fishery species, were usually found along the Albanian shore.

ISSN:1125-0003    

DOI:10.1080/11250009809386876

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor