摘要:

Large variations in the number of female adult salmon spawning in the Girnock Burn each year (range 28–127) produced smaller variations each year (range 2900–5600) in the number of juvenile migrants. The relative constancy of the parr migrations was achieved by changes in their age composition. There may be no advantage in allowing ova deposition to exceed a level around 200 000 (3.4 m−2) in the Girnock Burn, which would give rise to an average of about 4000 juvenile migrants (0.07 m−2) per season. Large numbers of ova (up to 12.5 m−2) did not decrease the number of juvenile

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04771.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Comparisons were made of the mortality, growth and condition factor over a 50‐day period of eleutheroembryos, alevins, 2‐month fry, 4‐month fry and 1 + rainbow trout,Salmo gairdneri, in water of three qualities–Birmingham tap‐water, 50% and 100% settled effluent from percolating filters (Minworth Effluent Treatment Works) when dissolved oxygen levels were maintained near 100% ASV.There was no significant mortality among life stages in control tap‐water but the LT50 values of life stages in both 50% effluent and 100% effluent revealed significant differences. Inter‐treatment comparisons showed similar mortalities of eleutheroembryos, of 2‐month fry and of 1 + fish in the three treatments but LT50 values of 4‐month fry showed significant differences. Growth rates of 2‐month and 4‐month fry were suppressed in both effluents after 7 days and there was a significant deterioration in theKfactor of these life stages after 14 days. Predicted toxicities (the sum of the proportions of the 48‐h LC50 of the individual poisons to rainbow trout) were compared with the observed toxicity in 50% and 100% effluent. The relevance ofin vivotesting in comparison to predictive

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04772.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

On a commercial fish farm in Western Scotland, smolting Atlantic salmon,Salmo salarL., showed no major changes in serum thyroxine (T4) levels in the spring. In contrast, serum T4 levels in smolting, wild salmon, trapped as they left the Girnock Burn, Aberdeenshire, varied markedly over this period. Serum T4 levels were correlated with the stream discharge rate pertaining as the fish left the stream. Levels in migrating, smolting fish were higher than those in fish captured above the fish‐trap by electro‐fishing. In a stream channel, serum T4 levels in smolting fish caught previously in the fish‐trap were rapidly elevated by exposure to increased water‐flow, whereas levels in fish previously captured above the trap remained substantially unchanged. Serum T4 levels in salmon parr leaving the stream in autumn were generally lower than those in smolting fish leaving in spring and were not demonstrably affected by stream dischar

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04773.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Densities of salmon, trout and grayling were assessed in Scottish streams by systematic counting by underwater observers, where the water was greater than 1 m deep, and by using electrofishing equipment in adjacent shallower areas. Tests of the efficiencies of the two methods are described. Applications have included the estimation of production of trout, grayling and young salmon at a site on the River Tay and predicting the salmon smolt run of the River Tilt, and these applications are briefly described. The most suitable period for visual counting was summer, as at water temperatures of less than 15° C fish were hiding among stones in the stream bed. Wet weather hampered both electrofishing and visual counting

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04774.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

When hungry salmon were offered a simulated (unattainable) swarm of krill with high central density, the density of the region first attacked increased with increasing attack readiness (measured as snout contacts). When allowed to capture krill in a range of prey densities, hungry salmon captured krill most successfully (in terms of capture/contacts) in the lowest density and less efficiently with increasing densities. However, salmon still captured a greater number of krill in a given time in high compared to low densities. When salmon in three different hunger states were exposed to a simulated swarm of krill, those with the lowest hunger level most often attacked the lowest prey densities first. Salmon with a high hunger level most often attacked the highest prey density first. Those fish with a moderate hunger level chose an intermediate prey density. This behaviour can be interpreted as a hunger‐dependent feeding strategy. The ways in which swarming of the prey might influence capture by the predator are considere

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04775.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Landlocked salmon derived from a wild population of stunted ouananiche and bred in the laboratory showed signs of smoltification, but adaptation to sea water was slow and limited to 11% of the fish tested. Sea water survival was not related to initial size, within the range used, nor to sex, age (2 + yearsv. 3 + years) or spawning history.Freshwater ouananiche had fewer gill chloride cells than anadromous smolts of similar size in fresh water. Anadromous smolts showed an increase in chloride cells after adaptation to sea water and those ouananiche which successfully adapted to sea water had a greatly increased number of gill chloride cells.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04776.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Fish mortalities in the River Nidelva, South Norway in 1978, were suspected to be caused by Gas Bubble Disease. In June 1980, the hydrological situation occumng in the Nidelva in 1978 was reconstructed, and the effects were analysed by keeping fish in cages. Examination of the dead fish showed that most were killed by Gas Bubble Disease. The results also showed that brown trout,Salmo trutta, was the least tolerant, and eel,Anguilla anguih, was the most tolerant to dissolved gas supersaturation. Only fish kept near the surface were killed while fish kept at 3 m depth were mildly affected due to hydrostatic pressure compensation. In contrast to the situation in 1978, few of the wild fish were killed during the experiment in 1980.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04777.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Apparently healthy, feral goldfish,Carassius auratusL., were collected from a pond in Cambridge, Ontario from March until November 1981, and during April 1982. Based on histological examination, oocyte development was divided into five stages and the reproductive cycle into five periods. The origins of oogonia and the atresia process were examined. The gonadosomatic index (GSI) was found to be an accurate indicator of ovarian activity in the feral population. Based on the GSI, proportion of various oocyte stages and egg size, females older than 2 years appeared to spawn during two periods, May to June and late August; 2‐year‐old fish spawned in the first period. There was a reduction in the density, abundance and nuclear diameter of presumptive pituitary gonadotrops in early August, after the completion of ovarian development and before the completion of spawn

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04778.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Cichlasoma nigrofasciatum, the convict cichlid, is a biparental, substrate‐spawning, Central American cichlid. Male‐female pairs were kept for 4 months on one of three food rations: high–1 g food daily; medium–1 g three times per week; low–1 g per week. The number of spawnings was directly related to the food ration. The fecundity of the females on the low and medium rations declined. At all rations the inter‐spawning interval and egg size increased during the experiment. Egg size was positively related to ration and the length of the inter‐spawning interval, but the latter was inversely related to ration. Females on the high ration grew in weight while those on the low ration lost weight. Histological examination of the ovaries at the end of the experiment suggested that low rations reduced the proportion of oocytes that become vitellogenic. At the end of the experiment, the total, gonad and liver weight of females at a given length were significantly related to ration. No similar, significant effect was found for the males, although growth in length of the males was related to ration. Ration had no detectable effect on the histological appearance

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04779.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

This study is concerned with functional organization of some of the blood pathways in the gill filament of the flounder,Platichthys flesusL. The existence of two independent vascular pathways has been confirmed. The blood from the efferent filament artery (EFA) enters the central venous sinus (CVS) through very small blood vessels which are characterized by the presence of sphincter‐like structures. The existence of an independent chamber of the CVS mainly full of white blood cells provides evidence of an independent lymphatic system connected to the CVS. Gill rays support the afferent side of a gill filament whereas plasma and an extensive network of nutritive blood vessels in the CVS supports the efferent par

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1984.tb04780.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY