摘要:

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hakeMerluccius gayilanded at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes forGrillotia dollfusi, Hysterothylaciumsp.,Clestobothrium crassicepsandAporocotyle wilhelmi. More use should be made of the information on whole parasite assemblages including, for example, patterns of co‐occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co‐occurring taxa in community assemblages would remain undet

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01452.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The von Bertalanffy growth function has limitations for describing the growth of fishes in seasonal climates. In the present work, a new equation is proposed where the growth parameter k is substituted by a function related to monthly water temperatures. The computer program GROWTHS was developed to fit and simulate the growth for seasonally varying temperatures. Examples for natural populations ofBarbatula barbatulaandCottus gobioare presented.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01453.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The quality of the surface water of Gotland (Sweden) streams was good, and did not limit sea trout egg‐to‐fry (ETF) survival. The oxygen concentration of the interstitial water was positively correlated to the permeability of the stream bed, and to the geometric mean diameter of the substratum. When the oxygen at 15 cm inside the stream bed was undiminished from surface values, the permeability of the stream bed was at least 6000 cm h–1and the geometric mean diameter of the substratum at least 15.0 mm. When the interstitial oxygen concentration increased, the interstitial ammonium concentration decreased, the NO2concentration remained stable and the NO3concentration increased. The ETF survival up to hatching was highly dependent upon the oxygen concentration of the interstitial water. For survival from hatching to emergence, the geometric mean diameter of the substratum was the most important factor. ETF survival>50% was observed where the interstitial oxygen concentration averaged at least 10mg I‐1, the substratum permeability at least 2000cm h‐1and the substratum geometric mean diameter at least 15 mm. Other factors, such as overdigging and drying out of the spawning grounds could increase the ETF

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01454.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A modification of the graphical Costello method is proposed for the analysis of stomach contents data. The new method allows prey importance, feeding strategy and the interand intra‐individual components of niche width to be explored using graphical presentation. The analysis is based on a two‐dimensional representation of prey‐specific abundance and frequency of occurrence of the different prey types in the diet. The paper describes the new method and the parameters therein, and also present some examples of the utilization of the method. The method may be particularly well‐suited for the examination of predictions made from optimal foraging, competition and niche t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01455.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The hypothesis that stream salmonids from habitats with low food density will be more aggressive than conspecifics from habitats with higher food density was tested through behavioural observations of wild‐caught young‐of‐the‐year brook charrSalvelinus fontinalisin aquaria. Standing stocks of benthic invertebrates in a high food density habitat were more than double those in a low density habitat and charr from the latter were significantly smaller than those from the former. Charr from the low food density habitat were significantly more aggressive, as indicated by nipping attempts within pairs, than were those from the high food density habitat. Both populations were genetically isolated and food density differences seemed to be related to persistent features of their habitats. This suggests that the observed behavioural differences may have both genotypic and phenotypic Co

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01456.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

In the catfishHeteropneustes fossilis, 0.5μg g‐1B.W. mGnRH‐A alone or the low dose of 0.05 μg g‐1B.W. in combination with pimozide [a dopamine (DA)‐receptor antagonist, 5 or l0μg g‐1B.W.], caused a preovulatory surge in plasma gonadotropin (GTH) and induced a high rate of ovulation. The ovulatory response of the catfish to the low dose of mGnRH‐A when given alone was not effective in the early (July) but was effective in the late spawning season (August). Plasma GTH response to these treatments showed seasonal variations. Pimozide administration potentiated the response to mGnRH‐A in a season‐dependent manner, being effective only in the prespawning and spawning phases. Pimozide treatment alone did not affect plasma GTH. These observations suggest that the release of GTH from the pituitary is subject to seasonal differences in the sensitivity of the GnRH system and the degree of its modu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01457.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The length, age and growth rate were investigated for downstream migrating male and female eels in the unexploited Burrishoole system, western Ireland. Significant differences were found in the age and length at migration with the larger, older female eels also showing faster annual growth as early as the first year in fresh water. Female eels normally migrated at lengths from 40.5 cm, exceptionally to 92.9 cm, and male eels at lengths between 28.9 and 46′0 cm. Back‐calculation showed an irregular pattern of fast and slow annual growth. Mean annual growth increments were almost always greater for females than for ma

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01458.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Temperature regimes of 17 ± 1°C and 21 ±1°C early in development of pejerreyOdontesthes bonariensisproduced nearly all females, whereas at 25 ± 1°C variable, sometimes male‐biased sex‐ratios were obtained. The critical period of thermolabile sex determination seemed to occur between 25 and 50 days post‐hatch (about 11 and 21 mm s.i.) at low temperatures (17–20°C) and between 0 and 25 days (about 7 and 15 mm) at high temperatures (22–25°C). The likelihood of expression of temperature‐dependent sex determination in natural populations and the possible adaptive significance of environmental sex determination in pej

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01459.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

PikeperchStizostedion luciopercafrom two different water areas off the Finnish south coast were affected by three types of fin abnormalities: fin anomalies, acute fin erosion (fin rot) and healed fin erosion. Fin erosion occurred at high prevalences at both areas, while fin anomalies occurred mainly in the area polluted by sewage.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01460.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The duration of one synchronous cleavage cycle (τ0) inClupea harengus membrasat different temperatures (T) was given by: (logτ0)= 2.4349–0–0684T forT=0.9–13°C, and (logτ0)= 1.61010–oooit for

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01461.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY