摘要:

Temperature and salinity tolerances ofTilapia rendalliwere determined experimentally. Results indicate that they are tolerant over a wide range of temperatures (11‐37°C), but are incapable of surviving in salinities above19‰ The maximum salinity tolerance is at temperatures between 20–28°C. The osmotic concentration of the blood rises from 255 mosmol/1 in freshwater to 340 mosmol/1 in a salinity of 19‰T. rendalliis restricted to the warmer waters of the Zambezi river system in central Africa and southwards to the Pongolo river, as well as certain tropical and subtropical brackish water lagoons and lakes. Evidence from these experiments suggest that the distribution ofT. rendalliisgoverned by both temperature and

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04665.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The reproductive cycle ofCoregonus lavaretus(L.) in Loch Lomond, Scotland, was investigated by monthly sampling. Spawing takes place during the first 3 weeks of January, on offshore gravel banks. Males congregate on the spawning‐grounds throughout the spawning period, while ripe females cruise in unisexual shoals in deeper water. Individual females migrate to the spawning‐grounds as ovulation takes place, spawn, and return to deep water. After spawning, the gonadosomatic ratio and somatic condition factor of both sexes decrease until June or July. Gonad recrudescence occurs in males between July and October, and in females between July and December. The somatic condition factor of both sexes rises from its minimum in June or July to its maximum in September. A competitive protein binding assay was used to determine cortisol levels in 0–1 ml plasma samples of individual fish. The lowest cortisol levels occurred in fish caught by seine‐netting and killed immediately by anaesthesia in MS 222 (Sandoz). Seine‐netting and killing by concussion induced higher cortisol levels, in the range of 3–5 ng/100 ml. Cortisol levels in fish caught by gill‐netting for 18 h were 3–6 times higher than in seine‐netted fish, and the method of killing was immaterial in this case. The length of time spent in the gill‐net had no significant effect on cortisol level, but maintenance of the fish in aquaria for 24–80 h elicited high cortisol levels of over 50 μg/100 ml. Post‐mortem delay before blood‐sampling resulted in lowered cortisol levels. Seasonal variations in cortisol level were determined in gill‐netted fish throughout the year, and in seine‐netted fish when available. Cortisol levels were high in both sexes in September; and very high in ovulating females caught on the spawning‐grounds, though not in ovulating females

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04666.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

A circuit for a pulsed d.c. fishing machine is described which represents substantial advantages over a previously published design. The present circuit has been fully field tested and is giving satisfactory service in routine fish population sampling in high conductivity water (up to at least 2000 μS/cm)

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04667.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Production and food intake by an herbivorous pupfish population (Cyprinodon nevadensis amargosae) living in the outflow of a thermal artesian well (Tecopa Bore) near Death Valley, California is described. Water issues from the ground at 47.5° C and cools 8.12° C before leaving the study area 300 m from the source. High stream temperatures restricted the pupfish population to some 41 % of the study area, with a resulting mean density of 89 individuals m−2(range = 13 to 196m−2). Biomass estimates ranged from 7 kcal m−2to 42 kcal m−2. The mean annual standing crop of pupfishes (24 kcal m−2) turned over about five times annually. Growth rates were highest in juveniles (♂= 9.5% day−1) and slowest in large adults (♀= 08% day−1). Monthly production ranged from 22 kcal m−2in September to 3 kcal m−2in July and August. Pupfish in Tecopa Bore fed on algae and detritus, ingesting 1941 kcal m−2yr−1or 17.5% of the annual net primary production. 119 kcal m−2yr−1was deposited in growth. This latter value is approximately ten times greater than values previously reported for large carnivorous fishes but is comparable lo values reported for herbiv

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04668.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The factors influencing the selection of food by flounders,Platichthys flesus(L.), have been investigated by analysing collections made in the Severn Estuary for 1 year and the results of experiments. Flounders measuring between 6–0 and 35 cm fed heavily on the polychaeteNereis diversicolorin February and on the amphipodGammarus salinusbetween February and April. Thereafter these species were replaced by the mysidNeomysis integerwith the decapodCrangon vulgaris.Flounders shorter than 6.0 cm, fed mainly onNeomysis integerregardless of month. Numerous factors were involved in the choice of the food including (1) the maximum and minimum length of prey, (2) its spatial distribution in the water column, (3) its degree of concealment, (4) its motility and ability to escape predation, (5) conditioning of the flounders for certain foods, (6) the fish's swimming speed and (7) the turbidity and temperature of the water.Although the average length of ingested prey remained unchanged as the fish grew in size, an increase in the maximum and minimum lengths was observed. The percentage of stomachs that contained no identifiable remains in flounders greater than 6–0 cm averaged 80–95 % during part of the winter and 60% in the summer and between January and March. These changes partly reflected the influence of low water temperature on the metabolic rate and availability of prey. The dry weight of the stomach contents in flounders longer than 6–0 cm was lowest in winter but high values were recorded in the spring. This latter feature was probably because the rate of feeding was greater than that of digestion. During the summer, under more normal feeding conditions, the weight of the stomach contents remained relatively low compared to other fish populations. Flounders shorter than 6–0 cm always contained more food in their stomachs on a unit weight basis than larger individuals, reflecting metabolic rate and hunting e

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04669.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Sea trout were sampled by shore seining in the sea lochs of the west coast of Scotland between 1970 and 1974, This area is of special interest because of the indentation of the coastline and the varying degree of freshwater and marine influence in the sea lochs. The majority of fish caught were in their first year after smolt migration. These post‐smolts were caught mainly in May and June, after which the number of trout present was low until fish at the ‘whirling’ stage appeared in the catches at the end of August, continuing through to the following spring. An additional recruitment of mainly unsilvered young trout from the rivers to the sea lochs was found in the autumn. Age and sex composition of both spring and autumn recruits, and of mature fish, were investigated and compared.A total of 3228 sea trout were tagged, with 311 recaptures. These recaptures supported the evidence from smolt trapping and beach seine catches that, in the first post‐migration year, the smolts migrate from the rivers from late March to early May, they then migrate from the sea lochs in May and June and return in late summer and

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04670.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The burrows of the red band fish,Cepola rubescensL. were studied. They were located In sublittoral mud some 17m below C.D. off the coast of Lundy Island. The burrows were vertical to a depth of 60 cm, the same length as the fish, and had a diameter of 6–8 c

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04671.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Young‐of‐the‐year (class 0) and yearling (class 1) striped mullet,Mugil cephalus, were collected from Sapelo Island, Georgia from May 1970 to June 1971 to study the development, seasonal abundance and relationship of environmental variables to parasitic populations. The number of species of parasites increased with age of the host. Initial infection appeared to be influenced by closeness of association of mullet age classes, by the period of abundance of a parasite on class I mullet and by the mobility of the infective parasitic stage. Fluctuations in intensity and prevalence of a parasite on class 0 mullet were similar to those of class I mullet after the initial infection.Ancyrocephalus vanbenedeniiwas first observed on class 0 mullet in March. Intensity was high on both classes in spring and on reproductively active mullet in late autumn. Prevalence on both classes was above 80% except in late summer.Polyclithrum mugiliswas not observed on class 0 mullet until August even though intensity and prevalence on class I mullet was highest during early spring.Gyrodactylus mugelusdid not occur on class 0 mullet but appeared on class I mullet during late summer.Microcotyle psuedomugiliswas observed on class 0 mullet in early summer andMetamicrocolyla maeracanthain October. Both species occurred but at a low intensity on class I m

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1976.tb04672.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY