摘要:

A multi‐species demersal fish stock was studied from April 1969 to July 1970. The common species are described in this paper and consist ofCarcharhinus sealei, Rhynchobatus djeddensis, Dasyatis kuhlii, Rachycentron canadum, Psettodes erumeiandAriussp. With the exception ofRachycentron canadum, these fish were available throughout the year and some coincidence of increased availability was noted in August/September.Psettodes erumei, the commonest fish caught, was most available in August/September, February/ March and June. The size and weight distribution of each of these fish is described. Morphometric results indicate that two fish,Dasyatis kuhliiandPsettodes erumei, exhibit sexual dimorphism, the females being larger and heavier than the males.Carcharhinus sealei, Rhynchobatus djeddensisandRachycentron canadumhave a nearly isometric growth exponent whereasDasyatis kuhlii, Psettodes erumeiandAriussp. have an allometric growth exponent. All fish were carnivores,Rhynchobatus djeddensis, Rachycentron canadumandAriussp. being primarily crustacean feeders,Dasyatis kuhliifeeding on polychaetes and crustaceans andCarcharhinus sealeiandPsettodes erumeifeeding mainly on fish. The increased number of all three bony fish noted in August/September (immediately prior to the short rains in October/November) is discussed in relation to feeding activity and the initiation of spawning activity. It is suggested that spawning inPsettodes erumeiandAriussp. is initiated in September, continuing possibly to February and then during the long rains (March/May) and the South East Monsoon the fish recover. It is also suggested that pregnant elasmobranchs may come inshore in greater numbers during the rains to give birt

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04036.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Eels (Anguilla anguilla) which were exposed to copper‐contaminated fresh water (30–60 ρg Cu/I) died with signs of vibriosis (Vibrio anguillarum).Eels kept in non‐contaminated fresh water (<6ρgCu/I) remained healthy.V. anguillarumwas shown to be present in the eels with symptoms of vibriosis. We suggestV. anguillarumis a common inhabitant of eels and copper can change a commensal association between fish and bacterium to one of pathog

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04037.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout (Salmo truttaL.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m2and 18.6 g/m2in the 2 year

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04038.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Samples ofGammarus pulexand dace,Leuciscus leuciscus, taken from the River Avon, Hampshire, at intervals over a period of 9 years were examined for the presence of theacanthocephalan. Pomphorhynchus laevis.Changes in the incidence and intensity of infection ofP. laevisin dace and inG. pulexand in the frequency distribution ofP. laevisin dace were used as indicators of the population size of the parasite. Throughout the period of observation, the parasite showed a similar pattern of distribution along the length of the river, although at some sites its abundance varied from year to year. Levels of both incidence and intensity of infection ofP. laevisin both hosts at one specific locality remained fairly constant over the 9‐year period, and the annual variations fell within the natural range of monthly variation over any 12‐month period. The frequency distribution ofP. laevisin dace also exhibited a similar pattern throughout the period. It was thus concluded that the population size ofP. laevishad not changed to any great extent over the 9 years. The factors responsible for this constancy are discussed in the light of conclusions drawn from earlier w

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04039.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

A 3 year survey of a lake, in which 120 roach,Rutilus rutilus, were examined revealed the presence of the plerocercoids ofLigula intestinalisin more than 90 % of the fish. The average number of parasites per fish was 4.2 although fish exceeding 32 g were not ligulosed. Gudgeon,Gobio gobio, of all sizes were affected. Implants of the plerocercoids into small roach, gudgeon and goldfish,Carassius auratus, were successful but not in the case ofPerca fluviatilis, Esox luciusandLeuciscus cephalus.The pathological effects of the plerocercoids on roach and gudgeon are described.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04040.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Evidence is presented which supports the hypothesis of a seasonal migration between the North Sea and the western English Channel. Fish caught west of Britain have a different length composition and there is some evidence of a North–South migration. Analysis of stomach contents shows that the species is a plankton feeder. Data on seasonal growth in young fish show the growth‐rate is most rapid between August and December; length‐frequency distributions of two year‐classes were bimodal. The use of the otolith burning technique revealed up to 35 check rings, as compared with the reported maximum age of 10 years. With the exception of ring numbers 1 to 3, it could not be established the rings were

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04041.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The primary immune response of brown trout (Salmo truttaL.) was studied after injections of two cellular antigens–Salmonella typhiH, flagellar antigen d, and human group ‘O’Rh+ red blood cells. Both intraperitoneal and intramuscular injections were employed. Agglutinins and complement–fixing antibodies were produced toS. typhiand haem–agglutinins to human ‘O’ red blood cells. Maximum titres toS. typhiwere reached after 49 days in the case of both agglutinins and complement‐fixing antibody. Haem‐agglutinins reached a maximum value of 1 : 512 between 35 and 42 days. Haemagglutinins to human ‘O’ red blood cells were detected as early as 7 days after injection. Antibodies againstS. typhiwere found after 14 days. Natural haemolysins were present against horse, sheep and human groups ‘A’, ‘B’ and ‘AB’ but not with group ‘O’. No natural haemagglutinins were present to the six types of red blood cells tested. No precipitins were detected to eitherS. typhior human

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04042.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The effects of pinealectomy on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing activity were examined in the cyprinid teleost,Notemigonus crysoleucas, exposed to various photoperiod‐temperature regimes. In fish exposed to a long photoperiod‐warm temperature regime, pinealectomy resulted in a decrease in gonadal activity, in hypothalamic gonadotropin releasing activity and an increase in pituitary gonadotropin potency. Fewer gonadotrophs were present in the pituitary of sham operated fish than in the pituitary of pinealectomized fish. Ovarian development was more rapid in sham operated than in pinealectomized fish exposed to a long photoperiod–low temperature regime. Pituitary gonadotropin activity was also greater in shams than in pinealectomized fish. A short photoperiod‐warm temperature regime retarded ovarian development inN. crysoleucas.Pinealectomy reversed this trend. Gonadotrophs made up a greater area of the pituitary in pinealectomized fish than in shams under these conditions. Gonadotropin potency of the pituitary and hypothalamic gonadotropin releasing activity were also greater in pinealectomized fish than in shams. The area of the pituitary occupied by gonadotrophs was greater in pinealectomized than in sham operated animals maintained on a short photoperiod‐low temperature regime. Pituitary gonadotropin activity was also greater in pinealectomized fish as compared to shams. Pituitary gonadotropin potency varies diurnally in animals maintained on both short and long photoperiods; the rhythm of variation differs depending on photoperiod. Pinealectomy alters the diurnal rhythm of pituitary gonadotropin potency in animals exposed to both long and short photoperiods. It is concluded that pinealectomy has a pronounced effect on reproductive activity inN. crysoleucas.The effects of pinealectomy on reproduction vary with photoperiod, but are mediated via the hypothalamus and pituitary. In fish exposed to long daylengths the pineal favours reproductive activity, but the epiphysis retards reproductive processes in animals maintained on short pho

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04043.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Oxygen uptake rate by rainbow trout red cells was measured in the temperature range 5° to 40° C. Between 5° and 20° C there was a steady increase in rate and at 20° C a maximum rate of 2.5 μl O2/min/ml red cells occurred, followed by a decline in the rate as the temperature increased. A morphological investigation of the red cell was conducted and possible functions of the nucleus in fish red blood cells are disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04044.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Rainbow trout (Salmo gairdneriRichardson) were subjected to 15 min anaesthesia with unbuffered MS 222, neutralized MS 222 and benzocaine with and without physical stress. Blood samples were taken through cannulae inserted into the dorsal aorta. The Hct values and Hb concentrations increased with all the anaesthetics, which also caused swelling of erythrocytes. The initial values were restored within 4–12 h of recovery. Each anaesthetic elevated the blood lactate concentration, but the initial level was regained within 12 h. The blood glucose level decreased the most during anaesthesia with unbuffered MS 222, but the initial level was rapidly restored. Benzocaine caused the least hypoglycaemia during anaesthesia, but the subsequent hyperglycaemia, as in the fish anaesthetized with neutralized MS 222, lasted 24 h. Neutralized MS 222 and benzocaine elevated the plasma K + concentration more rapidly than unbuffered MS 222. The initial levels were regained in 4 days. All anaesthetics raised the Mg++concentration.The Po2in the dorsal aorta decreased during anaesthesia with unbuffered MS 222 by about 85 mmHg, while the Pco2increased by about 1.5 mmHg. Their initial levels were regained within 20 min. During anaesthesia the pH value decreased by 0.3 units and returned to the initial value within 2–4 h of recovery. MS 222 seemed to be an asphyxi

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb04045.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY