摘要:

Movements of resident brown trout (age 2+ to 9+ years) and young Atlantic salmon (age 1+), stocked as fry, were studied in July, August and September in a coastal stream in northern Norway. Between 85 and 89% of the brown trout were recaptured in the study area (346m, 1326m2) within 45m of their release point throughout the investigation period. Most specimens had moved less than 150m. Trout movements were related to local variation in density. Trout occupying those sections of stream with the lowest fish densities (5.3–10.9 fish 100m−2) had a significantly lower movement rate than fish from sections with densities between 13.7 and 31.5 fish 100m−2. Trout that moved from their marking section were significantly larger than specimens that did not leave their original site. There was a significant correlation between permanence of station each month and the mean water level that month. The majority of the trout (47%) were caught at undercut stream banks or at sites in the proximity of these. A decrease in water level during the study period resulted in a high loss (36%) of such habitat, probably forcing some individuals to move. The recapture data indicate that the trout population consists of one small (c.15–20%) mobile, and one large sedentary component.Young salmon displayed high station permanence in July and August (93% and 96%). However, in the autumn they exhibited a significant downstream movement, and only 73% were recaptured within their release section. This movement was significantly higher for larger specimens, and is thought to occur because of a pre‐winter change in habitat, initiated by a decline in stream temperature. In contrast to trout, salmon in sections containing the lowest densities (22.0–25.0 fish 100m−2) did not show significantly lower movement rates when compared with salmon at higher densities (32.2–46.3 and 51.8–60.6 fish 100m−2). The spatial distribution of young salmon indicated the formation of territorial mosaics over the stream bed, which are thought to reduce intras

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05404.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The ectoparasitic digenean trematodePrototransversotrema steeriwas observed to infect a wide range of estuarine fish species of southern Queensland. The intensity and incidence of trematode infections onMugil cephalushosts were recorded and appeared to alter with the estuarine movement of the sea mullet host.Highest trematode population densities were present on post‐spawningM. cephaluswhich had recently traversed brackish estuarine waters. Similarly, the highest prevalence of external ‘red spot’ lesions was also recorded from such fish.The degree of complicity betweenP. steeriand ‘red spot’ bacterial pathogens was examined and is discussed. ‘Red spot’ or ‘ulcer disease’ is presented as a disease of multiple aetiology. It is suggested that some ectoparasites and a variety of primary and secondary bacterial pathogens may interact with environmental and behavioural factors to determine the prevalence of external lesions within each affe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05405.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Optimal conditions for the induction of triploidy in two different species of tilapia,Oreochromis aureusandOreachromis niloticus, were determined using either heat‐shock or cold‐shock techniques. These treatments were applied at conditions that were separately determined for each species. Embryos of these two species were found to differ in their response to heat‐shock, but not to cold‐shock treatments. The yield of triploidO. niloticusembryos induced at 40.5°C at the zygotic age of 3‐5 min did not exceed 13%, in contrast to 60% obtained inO. aureus(heat‐shocked at 39.5°C at zygotic age of 3 min). The possibility that the different responses of the two species to heat shock is maternally inherited was supported by the fact that the two‐way F1hybrids also responded in a similar maternally dominant manner. Although the induction of triploidy using heat shock was possible only within a narrow range of zygotic ages (2.5–3.5 and 3.5–4.5 min forO. aureusandO. niloticus, respectively), the induction of triploidy using cold‐shock treatment (11°C for 60 min) could be achieved within a wider range of zygotic ages (0–15 min). A satisfactory yield of troploids in the two species (50 and 60% inO. niloticusandO. aureus, respectively) was obtained using this technique. The possible interpretation of these results, that triploidy could be induced by interfering at two distinct meiotic cell‐division stages, is discussed. It is concluded that the cold‐shock technique is more advantageous for inducing triploidy inO. niloticus, whereas both cold‐shock and heat‐shock techniques a

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05406.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Blood coagulation inOreochromis mossambicuswas evaluated by determination of whole blood clotting times for traumatic and atraumatic blood samples and of intrinsic and extrinsic coagulation factors. Results indicate that this process is similar to mammalian coagulation, although clotting times were much reduced. In addition, species specificity to prothrombin activator was also indicated, which was not affected significantly by increased temperatures.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05407.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

An acoustic estimate of the number and biomass of a vendace stock (age>2 + years) in a deep basin of Lake Karjalan Pyhäjärvi was made in August 1985. The acoustic data were collected at night during the summer stagnation. The vendace were on the lake bottom during the day and rose by midnight to the hypolimnion; they did not rise to the thermocline or water layers above it. In the research area the mean number of vendace was 1900 fish ha−1and the mean biomass was 76 kg ha−1. Total vendace biomass was 151 in the whole 200‐ha resear

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05408.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The overwinter mortality rate of underyearling S2 Atlantic salmon parr (fish that will remain in fresh water for at least two years prior to smoltification) was almost ten times greater than that of S1 parr (fish that will smoltify after 1 year in fresh water) kept under similar conditions. The loss of condition (Kfactor) of the S2 parr was proportionally greater than that of S1 parr during the early winter months and this coincided with a marked lymphocytopenia and thrombocytopenia in the S2 parr. Limited evidence indicates that S2 parr have chronically elevated blood cortisol levels during the winter months. It is suggested that chronic stress resulting (in part) from nutritional deficiency has a debilitating effect on the defence systems of these fish. The ultimate cause of mortality in most cases was bacterial fin‐rot and/or fungal (Saprolegnia) infection. These findings are discussed in relation to the habitat requirements of overwintering salmonid fis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05409.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Experiments showed that minnows,Phoxinus phoxinus, sympatric with pike,Esox lucius, responded more vigorously to alarm substance than minnows from a population with no experience of pike predation in the wild. Minnows from the pike‐sympatric (Dorset) population were more likely to hide and less likely to risk feeding than their pike‐allopatric (Gwynedd) counterparts. The reaction to alarm substance in the pike‐sympatric population was further increased when it was presented along with the visual stimulus of a ‘stalking’ model pike. When the Dorset minnows experienced both alarm substance and the pike model together they reduced their inspection behaviour to a level below that of the Gwynedd minnows. Minnows from the Gwynedd (pike‐allopatric) population displayed increased levels of shoaling in the treatments in which alarm substan

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05410.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Acoustic signals emitted by the gudgeon are described and the context of sound production is considered.In aquaria, gudgeons produce creaking sounds of differing duration, which are always built up of single bursts. Each burst is composed of a series of rapidly repeated short pulses. Vocalization is correlated with the level of activity: it increases at higher temperatures and decreases when fish are disturbed. After acclimatization to the aquarium, fish which formerly showed a diurnal pattern of activity became active at all times of the day and night. Gudgeon called as a reaction to digging by other members of the group and a variety of disturbances, the latter including being touched or hindered by a conspecific or being frightened by the sudden movement of another fish. The fact that only certain interactions in a gudgeon shoal are accompanied by sound production is discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05411.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Fry of brown trout, Atlantic salmon, brook trout and lake trout were tested for downstream migration and critical velocities with a method of stepwise increasing water velocities. Each velocity was tested for 15 min before increase to the next step. Critical velocities for fry entering the free‐feeding stage, defined as the stage when the fry has resorbed its yolk sac and will have to ascend from the bottom gravel to catch food, were between 0.10 and 0.25 m s−1, varying among individuals and depending on species and water temperature. Downstream displacement started at lower velocities. Lake trout had the lowest critical velocity. Temperature influenced swimming performance considerably. On average, a 7°C increase in temperature resulted in a 0.05 m s−1increase in critical velocity. The fry actively searched out the low‐velocity niches in the channels. Flow‐sensivity gradually decreases with fry development; when the fry had reached a length of 40–50 mm they were able to tolerate water velocities higher tha

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05412.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The results of a beach seine survey of an East African mangrove creek are presented. The fish community of the creek is described and is compared with that of a nearby lagoonal site and with those described for other mangrove and estuarine systems. The species composition was found to differ substantially between the creek and the lagoon site, though diversity indices for the two areas were similar. Eighty‐three species of teleost fish werecollected from the mangrove area of the creek. This number is considered high in relation to comparable studies and is attributed to the constant high salinity (approximately 35%o) measured throughout the study period. Approximately 90% of the fish caught were juveniles. Plankton sampling was also carried out and representatives of 21 fish families were collected as larvae within the creek. Catches from both beach seining and plankton sampling in the mangrove areas were dominated numerically by resident clupeid and gobiid species. The majority of species, however, were considered to have a widespread distribution as adults. A discrepancy between the catch composition of larvae and juveniles suggests that species that use the creek as a nursery area enter the system principally at a post‐larval/ juvenile stage of development. No systematic spatial or temporal variation in the community structure was identified over the study per

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05413.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY