摘要:

An 8‐month survey of the Upper Zambezi River, its associated floodplain and marginal upland habitats yielded 16 catfish (Siluriformes) species, among whichSchilbe intermediuscomprised over half of the 3534 specimens. Generally catfishes were most abundant in floodplain and river channel habitats, but three species (Clariallabes platyprosopos, Synodontis macrostoma, S. nigromaculatus) were most abundant in the river channel, and three species (Amphilius uranoscopus, Chiloglanis neumanni, Leptoglanis rotundiceps) were most abundant or restricted within small tributary streams. Diet analysis revealed low pairwise dietary overlaps, but there was no statistically significant pattern of community‐wide niche segregation based on prey type. The 16 catfishes fell into four size/trophic guilds: large carnivores (Clarias gariepinus, C. ngamensis), medium‐sized carnivores (C. stappersii, C. theodorae, Parauchenoglanis ngamensis, Clariallabes platyprosopos, Schilbe intermedius), medium‐sized omnivores (Synodontis leopardinus, S. nigromaculatus, S. woosnami, S.sp. cf.woosnami), and small omnivores (S. macrostigma, S. macrostoma, Amphilius uranoscopus, Chiloglanis neumanni, Leptoglanis rotundiceps). No evidence of reproductive activity was detected in any of the catfishes during the survey period of falling and low water conditions. Although catfishes are not as highly valued for food as cichlid fishes, three species are significant components of local commercial and subsistence fisheries: the two largeClariasby virtue of their size, andSchilbeby virtue of its great abundance. Abundances of the heavily exploitedClarias gariepinusandC. ngamensisstocks appear to be lower in the Upper Zambezi compared with the Okavango floodplain

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01777.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Common species of kelp‐bed fishes including adult blacksmithChromis punctipinnis, adult senoritaOxyjulis californica, and sub‐adult kelp bassParalabrax clathratuswere collected from two separate and isolated rocky reefs at Santa Catalina Island, California, U.S.A. where giant kelpMacrocystis pyriferawas present. After tagging, groups of fishes were either returned to their initial collection site or displaced to an alternative kelp‐bed site to measure site fidelity and homing behaviour. No tagged fishes that were returned to their initial collection sites and subsequently resighted, exhibited any movement to another reef suggesting that these fishes have a limited home range, and handling during capture and tagging had no effect on site fidelity. Of fishes translocated to alternative kelp‐bed sites, up to 80% of tagged senorita and 100% of tagged blacksmith that were resighted had returned to the site of their initial collection, indicating that these species are motivated and able to relocate previously utilized areas when displaced. However, when young‐of‐the‐year and juvenile kelp bass were displaced, none were ever seen again suggesting that disruption of the relationship between a young kelp bass and its home site may influence

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01778.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Metamorphosed plaice and flounder were sampled in a small non‐tidal nursery bay with a non‐selective drop trap from April to August in 1991 and 1992. Post‐settlement patterns were mapped in time and space and related to wind stress and the distribution of a potential predatorCrangon crangonL. Both plaice and flounder had a patchy distribution at a sample scale of 1 m2. Plaice settlement coincided with timing of onshore winds in 1991 and 1992, while flounder settlement seemed to be unrelated. Plaice settled earlier than flounder and during the early phase of 1‐groupC. crangonimmigration. The first appearance of flounder occurred simultaneously with the peak biomass of predatoryC. crangon. Plaice occurred in the deeper part of the bay together withC. crangon, while flounder preferred shallow shore waters. We propose that different temporal (plaice) and spatial (flounder) strategies have evolved in order to minimize the risk of shrimp predation after set

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01779.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The movements of 24 hatchery‐reared Atlantic salmonSalmo salarsmolts, with miniature acoustic transmitters (pingers) implanted surgically, were determined after release in the coastal waters of Passamaquoddy Bay (mean tide range 6 m), New Brunswick, Canada, to describe the first stages of seaward migration. Automated pinger detection at fixed sites, and pinger location and tracking by boat were used. Post‐smolts left the release area rapidly, and the majority moved to open waters of the bay within several tidal cycles. Initially, post‐smolts moved with a seaward orientation on ebb tides and held positions on flood tides. Their movements into open waters were diurnal, and the timing corresponded with the state of the tide during which they moved through a narrow channel. Post‐smolts moved preferentially through this passageway with the aid of the tidal stream. Successful movements out through the channel occurred during ebb tides and any movements back in were during flood tides. Ground speed of fish moving through the channel was 4·2 body lengths s−1and faster than the tidal stream velocities in the channel. The relative velocity of fish swimming through the channel was 2 body lengths s−1. Post‐smolt movement was indicative of active, directed swimming with a reliance on ebb‐tide transport for migration through a coastal area with strong tidal currents. Some post‐smolts moved seaward directly with no apparent period of acclimation for the transfer to the marine environment, whereas others delayed their departure. These differences in behaviour were probably related to asynchrony in smolting when

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01780.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The menhadensBrevoortia gunteriandB. patronusare sympatric and morphologically similar. The two species are planktophagous and exhibited significant (P<0·0001) food resource partitioning, with phytoplankton predominating inB. patronusstomachs and zooplankton inB. gunteri.The branchial apparatus of both species is of the typical alosine form.Brevoortia patronushas significantly more branchiospinules per mm (x̄=19·47) and significantly longer gill rakers (x̄=13·35 mm) thanB. gunteri(x̄=14·11, x̄=12·01 mm respectively).B. patronusis characterized by a gill raker system forming a fine‐meshed filter capable of retaining smaller food items. The results support the hypothesis that food resource partitioning is related to different morphological features of the branchial

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01781.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Allozyme analysis was used to determine patterns of genetic variation and relationships within the genusValencia, a group with two allopatric species,V. letourneuxiinhabiting the Balkan Peninsula, andV. hispanicawhich is endemic to the Iberian Peninsula. Products of 25 gene loci were analysed withAK*,FH*,LDH‐1* andLDH‐2* monomorphic whenFundulus heteroclitus macrolepidotuswas not taken into account. Nine loci were diagnostic for both species of the genusValencia. Levels of genetic variation ofV. hispanica(P=0·416,He=0·118) andV. letourneuxi(P=0·160,He=0·040) were higher than values reported previously. High population subdivision (Fst=0·321) amongV. hispanicapopulations indicates a clear interruption of genetic exchange among populations. High genetic variation and differentiation exhibited by populations ofV. hispanicasuggest that a recovery program should be carried out with natural stocks from the same lo

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01782.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Karyotypes have been described in four Mediterranean species of the genusDiplodus(Teleostei, Sparidae),D. vulgaris, D. puntazzo, D. sargusandD. annularis. Chromosomes were mainly acrocentric in all butD. vulgaris, where certain chromosome pairs were subtelocentric. A remarkable intraspecific heteromorphism in the number of NOR‐bearing chromosomes along with a substantial interspecific variability in position of chromosomal Ag signals have been encountered. The presumed origin of multiple NOR‐bearing chromosomes inDiplodusspecies and variation of the NOR location is discus

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01783.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Seasonal changes in the geographic distribution of juvenile (ages 1–4) Atlantic codGadus morhuawere determined from research surveys conducted in the southern Gulf of St Lawrence during 1986–87, 1990–91, and 1994. From late June to early October, juvenile cod were most abundant in shallow water (225 km (each way). Age 3 and 4 cod migrated greater distances than age 1 and 2 fish. Some age 3 and 4 cod migrated as far as 650 km from their summer and early autumn areas. Although there was partial geographic segregation of juvenile and adult fish during summer and winter, all age groups were found together during the migration. No cod were present in the shallow waters (<80 m deep) of the south‐western Gulf during April due, in part, to later than average ice‐melt. Large numbers of all age‐classes were present in most of the south‐eastern Gu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01784.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Diel feeding patterns and daily food rations of five cyprinidsAmblypharyngodon melettinus, Barbus chola, B. dorsalis, B. filamentosusandRasbora daniconiusin two Sri Lankan reservoirs were studied based on diel surveys using an iterative method, MAXIMS.A. melettinusandB. cholahad single peaks of feeding whereas diel feeding patterns with two peaks occurred in the other three species. Daily food rations varied seasonally and with size of fish. The iterative technique used is reliably applicable for quantifying daily rations, and provides a means of linking trophic levels in natural populations of fish.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01785.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Mullet fry from Italian coastal waters are examined to ascertain ontogenetic changes in pigmentation, external morphology, anal‐fin ray counts, and morphology of the pyloric caeca and pharyngobranchial organ. The taxonomic utility of these characters is assessed. Intraspecific and ontogenetic variation in anal‐fin ray numbers do not make this a consistently reliable character for identification purposes. Pharyngobranchial morphology can assist diagnoses of larger fry or juveniles; however, pigmentation patterns are the most reliable characters for smaller fry. Pigmentation characters, which can be used in laboratory‐ and field‐based studies, require minimal manipulation of the fish and enable rapid identification of large numbers of specimens. These techniques are valuable for aquaculturists and fish biologists requiring more information on the identification, distribution and life history of m

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01786.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY