ISSN:0706-652X    

DOI:10.1139/f91-297

出版商:NRC Research Press    

年代:1991

数据来源: NRC

ISSN:0706-652X    

DOI:10.1139/f91-298

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Fish introductions in Africa have been made at various spatial scales from small fish ponds to the largest lakes, primarily to sustain or increase production, though some were to develop sport fisheries and to control unwanted organisms. Some introductions have fulfilled their objective in the short term, but several "successful" introductions have created uncertainties about their long-term sustainability.Lates niloticus,Oreochromis niloticus,O.leucostictus,Tilapia melanopleuraandT.zilliwere introduced into Lakes Victoria and Kyoga in 1950's and early 1960's; by the 1980'sL.niloticusandO.niloticusdominated the fisheries, having virtually eliminated a number of endemic species. In Lake Victoria, the loss of genetic diversity has been accompanied by a loss of trophic diversity; the transformation of the fish community coincided with profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. By contrast, the introduction of a planktivore,Limnothrissa miodoninto Lake Kivu and the Kariba reservoir has established highly successful fisheries with little effect on the pre-existing fish community or trophic ecology. The endemic species-rich African Great Lakes may be particularly sensitive to introductions. Species extinctions, introgressive hybridization and ecosystem alterations may occur following introductions.

ISSN:0706-652X    

DOI:10.1139/f91-299

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

At least 134 exotic and/or translocated fish species belonging to 34 families which were introduced to 29 of 33 European countries are documented. These include 35 species of Cyprinidae (introduced to 28 countries), 17 Salmonidae (28), 11 Coregonidae (12), 10 Cichlidae (8), six Centrarchidae (23), five Acipenseridae (8), four Ictaluridae (18), four Poeciliidae (11), four Percidae (9), four Mugilidae (1), three Catostomidae (6), three Gasterosteidae (5), two Anguillidae (3), two Atherinidae (2), two Clariidae (4), two Gobiidae (2), two Umbridae (6), two Pleuronectidae (1), two Thymallidae (3) and one species each of Anabantidae (1), Channidae (2), Clupeidae (1), Cobitidae 91), Eleotridae (1), Engraulidae (1), Esocidae (3), Mullidae (1), Osmeridae (1), Percichthyidae (1), Petromyzontidae (1), Polyodontidae (2), Siluridae (5), and Syngnathidae (1). True exotic species amount to 74 species/forms belonging to 21 families, of which 11 families are exotic for Europe. The remaining 60 species (21 families), are native in Europe and were translocated among various watersheds and/or countries. Most species were intentionally released since 1945 to enhance sport, commercial and subsistence fisheries, for fish farming and aquaculture, and for purposes such as mosquito, macrophytes and algal bloom control. Poor success was registered in most cases, along with adverse or unexpected effects on native fishes and their habitat.

ISSN:0706-652X    

DOI:10.1139/f91-300

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Biotas are constantly being reshaped by invasions. Introduction is now an added route to invaders. Impacts must be viewed against the background of massive changes in type, extent and quality of freshwater habits globally and in that freshwater fishes are almost living fossils. Also, old lakes and lacustrine fishes are highly restricted geographically. Lakes are young while rivers are old. Riverine, marsh and pond fishes are not well adapted to lacustrine conditions now widespread due to reservoir construction. Some Clupeidae and Cichlidae are lacustrine-adapted and highly productive. They have therefore made major impacts on fish yields in lakes and reservoirs. In tropical Asia and America, there have been a series of overlapping waves offish introductions during the past 150 years, culminating tin the tilapias from Africa. These fishes now dominate capture and culture fisheries in many countries. Fish introductions are a fait accompli and will continue. They must be realistically assessed and carefully monitored. Contrary to some predictions, introductions have not caused severe damage to indigenous species except when piscivores were used. Yields of indigenous fishes have apparently been enhanced in some instances. Parasites pose a serious threat and only an effective quarantine will ensure their exclusion.

ISSN:0706-652X    

DOI:10.1139/f91-301

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The inland waters of Australia have been colonized successfully by 20 species of freshwater fishes introduced to the continent, including 6 poeciliids, 3 salmonids, 4 cyprinids, 5 cichlids, 1 percid and 1 cobitid, all of which reproduce there in the wild. The ecological and genetic consequences of fish introductions and translocations have concerned scientists and water authorities since the late 1960's, although the earliest introductions of salmonids for sport were made towards the end of the 19th century. Impacts of introduced fishes, including hybridization problems, habitat and water quality alterations, competition for space and food, predation and the introduction of exotic parasites and diseases are reviewed. Emphasis is placed on sub-tropical and tropical species, since they appear to present the greatest threat to natural ecosystems. Problems in the translocation of indigenous Australian fishes between drainage systems to supplement recreational fishing are noted; a review of the Lake Eacham rainbowfish, supposedly brought close to extinction in its natural habitat by translocated Australian piscivores, demonstrates that unanticipated predator–prey interactions may result from the thoughtless addition of piscivores to an endemic community. A theoretical perspective on the assessment of candidate species for introduction and translocation is given, and areas of theoretical ecology that may assist in predicting future impacts of introduced species are discussed.

ISSN:0706-652X    

DOI:10.1139/f91-302

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The introduction of fishes into North America began in the late 1600's. The number of species has increased over the years, with pulses in the late 1800's and following the 1950's. By 1989, there were 45 established exotic fishes in the continental USA, and 16 in Canada. By 1989, the number brought into, invading, or transferred within Canada was 92 species plus 13 subspecies and hybrids. A special situation for Canada is the steady invasion from U.S. waters. Over the years, 38 such species have been identified. A variety of societal pressures led to the introductions, and the species introduced represent a number of realized or potential environmental impacts. Various international, national, state and provincial agencies or programmes have developed to investigate introductions and/or judge individual applications for the importation or transfer of live fishes. The number and nature of species being moved is still not well known. For Canada, 125 forms (species, hybrids, selected strains) which fit the new definition of Introduced are summarized by province and mode of introduction.

ISSN:0706-652X    

DOI:10.1139/f91-303

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Stocks of northern largemouth bass (NLMB),Micropterus salmoides salmoides, Florida largemouth bass (FLMB),M.s.floridanus, and both reciprocal F1hybrids were produced through natural spawning; the genetic composition of each stock was confirmed electrophoreticaliy, and experimental populations established. One set of experimental populations (P1 and P2) contained as broodstock equal numbers of adult NLMB and FLMB, whereas the other set (H1 and H2) initially contained equal numbers of adults of both reciprocal F1hybrids and both pure subspecies. Each year-class produced experimentally were sampled and individuals analyzed genetically to determine their parentage. Initially, much of the YOY production in P1 and P2 was composed of small FLMB that did not survive winter well; once naturally produced F1hybrids entered the breeding pool, most offspring were Fxhybrids, and the population became heavily introgressed. In H1 and H2 introgression began with the production of the first year-class. Within each year-class NLMB produced in all ponds were significantly larger than all other genotypes, but it appears likely that after only a few generations, production of pure NLMB ceases, all individuals being Fxhybrids. Results illustrate the potential negative impacts of introducing FLMB or hybrids between it and NLMB into waters within or contiguous to the native range of the northern subspecies.

ISSN:0706-652X    

DOI:10.1139/f91-304

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Stocking of non-native Salmoninae into North American waters began around 1870. Brown trout (Salmo trutta) from Europe established populations across North America and is the only successful inter-continental introduction. Introductions of native salmonids within North America but outside their native ranges have been common. Ecological effects of salmonid introductions. include competition, predation on native salmonids and other fishes, environmental modification through digging of redds in stream bottom substrates during spawning, and introduction of parasites and disease to native fish. Direct genetic effects from stocked salmonids are caused by interbreeding with native species. Indirect genetic effects may result through selective forces and/or a reduction of effective population size, genetic drift, and inbreeding. Management actions used to remove non-native salmonid populations include chemical reclamation and construction of barriers to movement. Salmonid stocking as a management practice is appropriate for species or population rehabilitation. Continued stocking of non-native salmonids should cease where viable native salmonid populations exist. New introductions of Eurasian species should not be made because effects are unpredictable. Aquaculture and the creation of transgenic fish pose special threats to North American salmonids. The era of widespread, intentional introductions of salmonids by man justifiably is drawing to a close.

ISSN:0706-652X    

DOI:10.1139/f91-305

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Patterns of mitochondrial DNA (mtDNA) variation have now been examined in more than 40 fish species. This work has established that mitochondrial genomes of fish show constrained size variation, but that genomes of closely related species often vary in size, suggesting that counterbalancing deletions and insertions act to stabilize genome size. Gene order and composition are also stable, but nucleotide sequences show rapid divergence. Populations of most fish species contain a few common mtDNA haplotypes and a spectrum of their rare mutational derivatives. The extent of genetic divergence among dominant haplotypes seems linked to environmental conditions with greater divergence in freshwater than marine species, especially those occupying unglaciated localities. Haplotype frequencies ordinarily show considerable local divergence, largely as a result of stochastic shifts associated with population founding events. Such divergence provides a basis for both the discrimination of local stocks and for the recognition of major genetic discontinuities reflecting past episodes of gene pool fragmentation. Analysis of hatchery stocks has often revealed their mtDNA divergence, but in most cases stocks are fixed for haplotypes which are also common in wild populations. There is, however, the opportunity to develop brood-stocks marked with rare haplotypes, permitting their recognition in nature over many generations.

ISSN:0706-652X    

DOI:10.1139/f91-306

出版商:NRC Research Press    

年代:1991

数据来源: NRC