摘要:

Rainbow trout,Oncorhynchus mykiss, were subjected to either physical stress (twice daily chasing to exhaustion for 5 days) or a period of 2 months of fasting. Following these treatments, the levels of catecholamines, adrenaline and noradrenaline, stored within the kidney and posterior cardinal vein (PCV) were determined. The ability of the catecholamine‐storing chromaffin cells to release catecholamines in response to cholinergic stimulation was measured using anin situsaline‐perfused PCV preparation.In the physically stressed fish, theconcentration(μg catecholamine g−1tissue) of noradrenaline within the anterior and middle thirds of the kidney increased; the concentration of adrenaline was unchanged in all tissues. Thecontent(μg) of noradrenaline or adrenaline, within the various tissues, was similar in both groups of fish with the exception of a higher noradrenaline content in the middle third of the kidney in the physically stressed fish. The total catecholamine content (μg catecholamine) of these tissues (kidney+PCV) was unaffected by physical stress.With the exception of a lower concentration of adrenaline in the middle third of the kidney, the concentrations of catecholamines were unaffected by fasting. There was a trend towards a greater content (μg) of noradrenaline within all of the tissue regions of the fed fish, however, a significant difference was only observed in the anterior third of the kidney. The content of adrenaline in the fed fish was greater in all regions of the kidney as well as the middle third of the PCV. The total catecholamine content (kidney + PCV) was lower in the fasted fish owing to significantly lower PCV and kidney masses.Prolonged physical stress caused a decrease in the responsiveness of the chromaffin cells to the cholinoceptor agonist carbachol (10−8to 10−4mol). The ED50(the dose of carbachol required to elicit a half maximal response) for catecholamine release was 0·96 ± 10−6mol carbachol in the physically stressed fish and 0·84 ± 10−7in the control fish. Fasting did not alter the pattern of catecholamine release. The ED50values were 0·96 ± 10−7and 1·24 ± 10−7mol for fasted and fed fish, respectively. Thus, a physical stress affected both catecholamine storage and release whereas fasting affected only storag

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01319.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Within a month of first feeding sibling juvenile salmon had developed not only large differences in size (up to fivefold in weight), but also significant differences in behaviour. Large fish remained in refuges (overhead cover) significantly longer after having been frightened. On leaving the shelters most small fish established individual territories on the bottom and. downstream of the shelters. The greater aggressiveness of small fish in a novel environment (from holding tank to experimental stream) was related to this apparent territoriality. The increased shelter residence time and delayed establishment of individual territories might be interpreted as greater caution in large fish, which are able to avoid risky situations due to their higher energy reserves. In contrast, smaller fish need to leave refuges more quickly and to establish individual territories in a novel environment.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01320.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Previous time series analysis on vendace population dynamics in Lake Pyhäjärvi, 1971–1990, revealed a 2‐year cycle in year‐class strength, implying powerful density‐dependent regulation. Here we have extended this analysis by using multiple regression models to test whether the recruitment series is influenced by density‐independent factors. We chose population size with a lag of 1 year as the density‐dependent factor; the density‐independent factors were the summer water temperature with a lag of 2 years (temperature sum for June, July and August, indicating the year‐class strength of predators) and the temperature‐derived length of the larval period of vendace. For the years 1972–1990 the coefficient of determination (r2) of this regression model was 0·77. We suggest that the basic mechanism producing a persistent 2‐year cycle of vendace in Lake Pyhäjärvi is the asymmetrical food competition between age groups. The abundance of predators in the lake and the warming of the water after the hatching of larvae in spring together determine the final year

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01321.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Although schooling behaviour is an important antipredator response of guppies (Poecilia reticulata) in Trinidad it is not known whether fish elect to school with particular individuals. Familiarity is a simple mechanism that could lead to non‐random associations within schools. In this paper we test the idea that prior experience of particular individuals influences the choice of partners during schooling. We show (in a laboratory study) that female guppies prefer to associate with familiar individuals. However, we are unable to detect any schooling preference for unfamiliar females from the same populatio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01322.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

At least four races of charr occur in Windermere, the largest natural lake in England: north basin and south basin autumn spawners, north basin and south basin spring spawners. This study examines racial differences between eggs and juveniles, and relates juvenile size and survival to egg size. There were no major differences between races for egg incubation times and the percentage of eggs hatching successfully, the latter being high (mean values 76–96%) with a negligible proportion of abnormal alevins (<0.8%). Although there were no significant differences in the lengths of the female parents, both eggs and alevins were significantly larger for the autumn spawners than the spring spawners. Size differences in alevins, especially live weight, were positively related to egg size but not female parent size. Mean percentage survival for juveniles attaining the independent feeding stage was higher for the progeny of autumn spawners (32%) than spring spawners (3%). Racial differences in the egg and alevin stages therefore appear to have a significant effect on subsequent survival, and could be ultimately responsible for the relatively small proportion of spring spawners (only 4–6%) in the Windermere population of ch

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01323.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

This article describes two small scale experiments designed to test whether variation in melanophore patterns could be used to identify individual juvenile salmonids that are too small for conventional marking methods. Three independent observers were able to identify 30 individual 0+ Atlantic salmon (Salmo solar) parr from photographs taken over an 8‐week period with 100% accuracy, on the basis of patterns of melanophores in the region of the eye and jaw. Counts of the number of melanophores in two particularly variable regions of the head of 14 newly‐emerged brown trout (Salmo trutta) from photographs of the same individuals taken on different occasions were strongly correlated. Eighty‐four per cent of the fry were correctly identified on the basis of spot number alone, without any reference to their patterns. Thus a combination of the number and position of head melanophores can be used for recognition of relatively large samples of very young salmonids. Problems with, and potential applications of this method are disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01324.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Groups of Arctic charr and rainbow trout were fed by using demand feeders and their individual trigger actuations registered with a PIT‐tag (Passive Integrated Transponder) system. Food was supplied at two reward levels, low and high, to five replicate groups of each species for 21 to 27 days. The reward level was defined as the amount of food obtained in response to a single trigger actuation. The effects of reward level on individual demand feeding activity and growth rale were assessed.As a result of high demand feeding activity, the daily food rations for trout were in excess of their needs at both reward levels. This can be ascribed to the fact that they compensated a low reward level by increasing their bite activity. In contrast, demand feeding activity in charr did not differ significantly between reward levels. Instead, resulting food rations were limiting and excessive, at low and high reward levels, respectively. The variation in bite activity between individuals (measured as their proportional contribution to the total number of trigger actuations within a group) for charr was significantly higher in the low‐reward treatment than in the high‐reward level. For trout, the variation in bite activity did not differ significantly between treatments. Differences in response to reward level are suggested to be due to the fact that the social hierarchy is weaker in trout than in charr; i.e. the differences in bite activity between dominant and non‐dominant individuals are smaller in trout. At both reward levels, the benefit of being dominant, measured in terms of growth rate was significant for charr but non‐significant

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01325.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Due to unfavourable conditions (declines in salinity and water oxygen content) in the spawning areas, there has been a considerable decrease in the Baltic cod stock since the beginning of the 1980s, and consequently a decrease in catches. In order to examine the feasibility of introducing yolk‐sac larvae in areas of low salinity to improve the stock, laboratory experiments were performed on the effects of salinity on the survival, level of activity and feeding ability of larvae. Yolk‐sac larvae from spawning cod caught off northern Gotland, Sweden, were exposed to four different salinities: 10 and 15%○ (salinities of the main spawning areas); and 5 and 7%○ (salinities in the Bothnian Sea and the Baltic proper respectively).The survival of yolk‐sac larvae was high at all salinities, even though there was an indication of higher mortality at low salinities in less viable larval groups. No differences were found in swimming speed or feeding ability at the four salinities, but a significant difference in vertical distribution was recorded. There were significant differences in survival, vertical distribution and feeding ability among larval groups, which indicates that larval quality or viability is of greater importance for larval survival than salinity, in the range

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01326.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The reproductive behaviour of two species of barbel (Barbus barbusandBarbus meridionalis) was investigated by means of aquarium experiments in several matings of six combinations. The reproductive behaviour of the two species appears to be similar and hybridizations were observed, showing that no complete behavioural barrier blocks the mating of the two species.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01327.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The distribution pattern of the palatal taste buds and their electrical response characteristics to amino acids were studied in five salmonid species: Arctic grayling (Thymallus arcticus), lake whitefish (Coregonus clupeaformis), Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and kokanee (Oncorhynchus nerka). In these fish the most dense taste bud populations were found on ridges in tine area around the palatine teeth. With the exception of lake whitefish, the ridges adjacent to the teeth on the head and shaft of the prevomer were also dense in taste buds, which appear to be largely responsible for amino acid detection. All species, except for lake whitefish, responded well tol‐proline (l‐Pro) andl‐α‐amino‐β‐guanidinopropionic acid (l‐AGPA), with thresholds at 10−8‐10−7and 10−5‐10−4M, respectively. These species also responded to varying degrees to hydroxy‐l‐proline (l‐Hpr) andl‐alanine (l‐Ala), believed to be agonists forl‐Pro receptors. In addition, kokanee detectedl‐phenylalanine,l‐leucine and betaine. Of six lake whitefish examined, only one specimen responded tol‐Pro,l‐AGPA andl‐arginine. We concluded that in these five salmonid speciesl‐Pro andl‐AGPA receptors play a major role in amino acid gustation, and further proposed a hypothesis that salmonids may have initially evolved these two gustatory receptors. With phylogenetic advancement, they gained greater response capabilities by (1) acquiring new receptor types, an

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01328.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY