摘要:

The ovum ‘membranes’ and the micropyle apparatus of mature, extruded ova ofFundulus heteroclituswere examined by scanning electron microscopy. The ovum is covered by a thin jelly coat comprised of a dense mat of 0.3‐0.5 urn fibrils, except for a 50–100 um fibril‐free zone surrounding the micropyle apparatus. The micropyle apparatus consists of a 50–100 um diameter funnel‐shaped vestibule, at the bottom of which is a circular aperture 4–5 μ in diameter leading to the micropyle canal which traverses the entire chorion layer. The inner micropyle aperture, 2–3 um diameter, apposes the inner ovoplasm mass.The chorion is the major protective coating of the ovum. It consists of a thin (0.4 μm) outer zone, a thicker (9–12 μ), lamellated inner zone with 4–10 lamellae, and sometimes an innermost crystalline zone, varying in thickness from 1–13 μm. The extreme variability in the structure of the lamellated and crystalline zones of the chorion suggests that generalizations concerning ovum

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05125.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Acute (120h) toxicity of the water‐borne carcinogen, dimethylnitrosamine (DMN) to adultFundulus heteroclitus(L.) at 20°C and 20.2%0salinity in natural seawater was determined. The LC‐50 values were 8300 mg/1 at 24 h, 5500 mg/1 at 48 h, 4700 mg/1 at 72 h, 3300 mg/1 at 96 h and 2700 mg/1 at 120 h.Gross lesions consisted of peritoneal and cephalic ecchymoses. Microscopic lesions included necrosis and sloughing of the gastrointestinal mucosa, haemorrhage and necrosis of the liver, and necrosis of taste buds, with severity and incidence being a function of DMN concentration. Acute pathological effects of DMN onFundulus heteroclitusconformed closely to those reported in other species exposed to this compound by respiratory, oral or parenteral route. DMN concentrations used in this experiment greatly exceeded those expected to be found under natural conditions, and this report is intended both to improve our understanding of DMN‐induced pathology in marine fishes and to provide further evidence of the consistency of acute lesions induced by DMN, regardless of test organism or mode of ex

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05126.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Between 1932–1947 and from 1960 onwards, elvers have been trapped near the mouth of the River Bann, Northern Ireland, and released into Lough Neagh. Each period of elver transport has been followed by a marked increase in the proportion of male silver eels migrating from the lough. Catches of silver eels were sampled on several nights each year from 1965–1974, and the lengths of a total of 20358 eels measured showed a progressive increase in the percentage of male eels from 9.3‐86.0 % during this period. Various reasons for this change were examined. The different ages at which male and female eels migrate to the sea was not important. There was no evidence to support the hypothesis that male elvers normally remain in estuarine conditions, and their transport to the lough was therefore unnatural. An increasing fishing effort for yellow eels, such as occurred following the introduction of trawling in 1960, would favour males since small eels were returned to the lough. It was not thought, however, that this was a major cause of the change in sex ratio. Instead, elver transport appeared to be directly implicated, possibly by the overstocking of Lough Neagh, and the phenotypic determination of progressively more male eels, but the evidence for this suggestion was inconcl

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05127.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Measurements of oxygen consumption and heart rate showed that the range of variation in metabolic rate for any given heart rate in fish is too wide for any significant correlation to be used as a measure of metabolism as in some other vertebrates. By defining the maximum oxygen pulse a precise relationship can be established between maximum metabolic rate and heart rate. From field measurements of heart rate by telemetry useful information can be gained on metabolic rates.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05128.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Petenia kraussiiSteindachner (Pisces: Cichlidae) was collected from Lake Valencia, Venezuela from April 1973 to April 1974. A total of 457 specimens were examined for stomach contents, and 471 were analyzed for length‐weight relationship, sexual condition including fecundity and parasitism.P. kraussiiis primarily a plankton feeder when small and utilizes benthic invertebrates after attaining about 10 cm standard length. The larvae of a benthic ephemeropteran,Campsurussp. (Hexigenidae) was the most important single food item with gastropods and fish eggs also being found consistently in stomachs. No mature male fish were found, and only 17 of 471 fish could be identified as males, while 157 were females. Gravid females contained an estimated mean of 6266 eggs and matured at about 18 cm standard length and 100 g live weight. It was not possible to determine age from either scale or otolith

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05129.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

In Lake NaivashaTilapia leucosticta(Trewavas) spawns throughout the year. Males attain maturity at 180 mm and females at 160 mm total length. Males predominate over females in the catches (sex ratio 1‐00 : 0‐51). Fecundity ranged from 320 to 1328 eggs with an average of 751. The relationship between fecundity(F)and total length (L), body weight(W)and gonad weight(GW)is:The length‐weight regression coefficient is near to the cube. There is little seasonal fluctuation in relative condition of the f

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05130.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Exploratory trawl data were used to define demersal fish stocks of Lake Malawi in terms of abundance by depth and area. The mean weight of the catch generally declined with increasing depth. A comparison of initial standing stock estimates and the yield from a commercial fishery over a 7 year period suggests a potential yield of less than half of the initial stock. Over 160 species of fish have been identified in the trawl catch of which over 80% by weight were cichlids. Some of the commonest species of cichlids are listed. The composition of the catch in the heavily exploited southern end of the lake has changed from one dominated by large species ofHaplochromissp. andLethrinopssp. to one dominated by smaller species.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05131.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The effects of oestradiol‐17β on the gonosornatic index, liver size, hepatic and body lipid levels in the cyprinid teleost,Notemigonus crysoleucas, were investigated. Administration of oestradiol to female TV.crysoleucasduring the gonadal preparatory and prespawning seasons stimulates increases in ovarian size. During the early spawning season oestradiol therapy results in a reduction of ovarian gonosomatic index. Oestrogen treatment of males causes a suppression of testicular growth. In female fish exposed to long (15‐5L/8‐5D) or intermediate (12L/12D) photoperiods oestradiol increases body fat reserves. At short photoperiods (9L/15D) oestrogen treatment of females results in body fat store depletion Low doses deplete and high doses of oestradiol increase body lipid reserves in male fish. The hepatosomic index increases in both male and female fish following oestrogen treatment. Oestradiol therapy during the gonadal preparatory season, but not during the prespawning season, increases total liver lipids. Thein vitroeffects of oestradiol on liver lipid and carbohydrate metabolism were also examined. Under the conditions used in these experiments, lipid depletion was observed in liver slices incubated with or without oestradiol. Pretreatment of fish with oestradiol before liver tissue was removed drastically reducedin vitrolipid depletion. Oestradiol retards the gluconeogenesis and glycogenesis seen in liver slices incubated in a hormone‐fre

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05132.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

A surgical operating apparatus for fish that is effective for cranial surgery is described. The fishes are secured with clamp‐arms which extend against the pectoral and pelvic girdles. The head is held by a plexiglass mouthpiece, designed specifically for the fish species under investigation. The mouthpiece is also responsible for gill irrigation. The use of the apparatus for the surgical pinealectomy of salmonids is describe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05133.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Gastric emptying time in the dab,Limanda limanda, has been studied using an X‐ray technique. The addition of 25 % barium sulphate to a test meal did not significantly affect the transit time. Lowering the experimental temperature from 16.4 to 8.5°C markedly decreased gastric evacuation time. An increase in ration size led to an increase in the time required to empty the stomach and also to increase the amount of food digested per unit of time. For any given ration size, expressed as per cent body weight, the larger the animal the longer is the time required for evacuation of that meal. We suggest that the food intake per day, as a percentage of live body weight, will be smaller for largerL. limandain the wi

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1977.tb05134.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY