摘要:

The biology of grey mullet,Mugil cephalusL., adult populations in a coastal lagoon in Sri Lanka is presented. The percentage of grey mullet catches increased with increasing salinity. The larger fish were found in the deeper areas and the relationship of total length to depth wasL= 8.4602e0.0058DwhereL= total length andD= depth (cm). The overall female to male ratio was 0.95 : 1.0 and seasonal variation in the sex ratio is considered to be caused by the differential timing in the spawning migrations of the two sexes. Males mature at 34.0 cm and females at 31.5 cm. The main spawning season was between January and May and it is hypothesized that the breeding season is geared to utilize the favourable time period, for growth of fry, in the lagoon. Grey mullet sheds its eggs in batches. Fecundity varied from 0.45 to 4.2 million in fish ranging in length from 32 to 56 cm and in weight from 0.7 to 2.2 kg. Fecundity was significantly correlated to body length and weight and gonad weight.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05806.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Peripheral blood and haemopoietic tissues of spleen and kidney of the icefish,Chaenocephalus aceratuswere examined using LM and EM techniques. The peripheral blood contained cellular elements from all the recognized cell lines usually seen in other teleost groups. Erythrocytes were very rare; when found, they were mature or senile and fragile. Thrombocytes of two morphologies, several cell types considered to be part of the lymphoid series and monocytes/macrophages were present. Two distinctive types of granulocytes also were found; their morphologies and granulation were so different from teleost granulocytes hitherto described that their identification was impossible.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05807.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Digestibility values are reported for a variety of diets fed to plaice. It was found that animal proteins were digested better than those from plant sources and the inclusion of indigestible carbohydrate (starch) led to a decrease in the efficiency of digestion and absorption of protein. The results of the digestibility trials were used to investigate the influence of various dietary parameters on gastric emptying and it was found that the gross energy content of the diet was the most important determinant of evacuation. The findings are examined in relation to published data on food intake by fishes and the implications discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05808.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Preliminary experiments were performed to determine the diurnal variation in cortisol, using trout which had been cannulated three days previously. These results indicated that cortisol levels were reasonably stable between 10.00 and 18.00 hours, thus permitting experimentation during this period without diurnal fluctuations masking the cortisol response. Uncannulated fish were exercised in a flume for 2 h at 1, 2.6 and 5 bl s‐1and plasma samples taken from groups of five animals at 15, 30, 60 and 120 min after the start of exercise and at 1½, 12 and 24 h after the exercise ceased. The cortisol levels in all cases were elevated after 15 min, but the magnitude of the elevation increased with swimming speed. At 1 bl s‐1the cortisol levels increased from 76.4 (± 20.4) to 129.2 (± 20.4) ng ml‐1[mean (±s.d.)]. At 2.6 bl s‐1the increase was from 72.4 (± 17.1) to 254.4 (± 34.4) ng ml‐1and at 5 bl s‐1the increase was from 69.5 (± 27.5) to 326.4 (± 39.0) ng ml‐1. The cortisol levels were stable over the exercise period and all groups recovered to baseline levels after 24 h, though the sample taken 12 h after the termination of exercise was elevated due to regular nocturnal increases in cortisol levels. There were no dramatic changes in blood sugar levels during and after exercis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05809.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Rainbow trout were exposed to sublethal phenol or non‐ionized ammonia concentrations or to hypoxia. Blood samples were taken after various exposure periods and the packed cell volume (PCV) value, the whole blood glucose concentration and the plasma cortisol and chloride ion concentrations measured. At low pollutant concentrations there were no significant changes in the blood components compared to control fish values. At higher concentrations the general response to the stressors was significant increases in the PCV value and the glucose and cortisol concentrations during the first few hours of exposure, followed by a gradual return to normal values in the subsequent exposure time. The increases in glucose and cortisol concentrations were approximately proportional to the pollutant concentrations no such correlation was found for the PCV values. No clear pattern of plasma chloride ion changes was found in any experiment. Levels of no acute effect, in terms of toxic units (TU) based on the pollutants’ 48 h LC50values, were estimated for phenol as 0.3 TU and for un‐ionized ammonia as 0.1 TU, using the plasma cortisol concentration measurements. The use of fish blood component measurements as general indicators of a stress response is disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05810.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Juvenile pink salmon,Oncorhynchus gorbuscha, in two test groups of differing hunger level fed continuously on live copepods, maintained at high densities, throughout 12 h feeding periods in the laboratory. Analysis of video films showed that mean feeding rates were initially (first 10 min) between 51.5 and 63.8 prey‐capture attempts (snaps) fish‐110 min‐1, but declined abruptly with increasing satiation to relatively constant levels of about 5.0 and 8.0 snaps fish‐110 min‐1, which were maintained during the subsequent 11 h of feeding. The data suggests that after the initial filling of their stomachs with food, juvenile pink salmon keep their stomachs full by feeding at a rate that balances the gastric evacuation rate of 18.6 mg prey h‐1at 11° C. Less than 15% of the fish's stomach contents need be evacuated apparently for spontaneous feeding to resume or occur. Increased hunger level (by increasing a pre‐test food deprivation period from 24 to 72 h) resulted in fish increasing their average feeding rate and thus their ration consumed from 23.6 to 39.8% dry body w

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05811.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Myxine ios sp. nov.is a seven‐gilled hagfish occurring on the continental slope in the eastern North Atlantic, off West Africa and southwest Ireland. The two populations overlap in morphometric and meristic character, but the Irish population is distinguished by having a white head and a whitish middorsal or midventral line. More material and collections from intermediate localities are needed before it can be determined if the two populations are distinct at the specific or subspecific level. The northern (Irish) population ofM. iosis believed to occur in the same geographical range asM. glutinosabut to live at greater depths.Myxine iosis compared withM. glulinosaL. andM. capensisRegan, the other two eastern Atlantic Myxine species; new data are given for these species, both of which are regarded as vali

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05812.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

We used an immunocytoadherence assay to monitor the response of antigen‐binding cells (ABC) in the peripheral blood of sockeye salmon,Oncorhynchus nerka, after immersion in, or intraperitoneal injection of,Vibrio anguillarumLS 1–74 bacterin. Both methods initiated an elevated ABC response in less than one day; this response persisted one week longer in the injected than in the immersed f

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05813.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The contrast discrimination ofGadus morhuaL. was studied by means of a cardiac conditioning technique. Fish were trained to respond to a projected pattern of spots and the contrast of pattern and background then reduced until the minimum contrast required to elicit a response was established. This was repeated at seven different background light levels to cover the range of light conditions naturally encountered by the cod. The minimum detectable contrast decreased with increasing light level to a minimum of around 2.0%. The contrast threshold curve showed a discontinuity at a light level of approximately 8.0 × 10‐6W sr‐1m‐2. This was thought to be linked to the change from photopic to scotopic vision. Significant differences were found in cod taken from two different locations. Overall, cod contrast detection compared very favourably with figures available for other species including man. Using the obtained contrast discrimination figures some estimates were made of the cod sighting distance of hypothetical targets under natural cond

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05814.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The introduction, establishment and subsequent history of a population ofLigula intestinalisin roach,Rutilus rutilus, of a small lake was studied over a period of seven years. The introduction is believed to be a natural, chance colonization achieved by the return of Great Crested Grebes as permanent residents. Within two years the parasite had infected 33% of the roach between 60–120 mm in size. It exhibited a pronounced seasonal cycle in infection. Fish were often infected when only a few months old in autumn, and young fish and parasites over‐wintered together. Parasite growth resumed in the following summer, when some further infections occurred. The majority of infected fish died in or before their second winter, possibly as a result of selective predation, but a small proportion survived into a third year. Dispersion of the parasite was close to random for most of the time. Multiple infections and slight over‐dispersion occurred only in summer months. Infections were scarcer in large fish, due partly to selective mortality of infected fish and partly to a change in the host diet. The pattern of seasonal infection compared favourably with other localities, but prevalence and intensity of infection were consistently lower, parasite dispersion closer to random and multiple infections much scarcer than elsewhere. Infection levels and parasite growth rates varied from year to year, but these annual fluctuations were irregular and showed no consistent pattern. TheLigulapopulation exhibited both regulatory and destabilizing features and there was no definite evidence that it was stable. It is suggested thatLigulais an opportunist species. It is endemic in some sites but in others, especially small lakes, the populations are unregulated and unstable and so persist for short periods only in a non‐equilibriu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05815.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY