摘要:

We tested two hypotheses that describe previously untested assumptions about the appropriate stage(s) for use in determining clutch sizes in darters. Three sequential stages of clutch/ovarian development are recognized: mature oocyte/ovary, ripening oocytc/ovary, and ripe oocyte/ovary. Mean ratios of clutch size to female length (relative clutch size, RCS) were significantly smaller and variances of RCS were significantly greater in ripe females when compared to mature and ripening females. Correlation coefficients for the relationship between clutch size and standard length (S.L.) were significantly greater for mature and ripening females than for ripe females. Mean clutch size, adjusted for the S.L. covariate, was significantly greater in mature and ripening females than in ripe females. Thus, we conclude that counts of eggs from ripe females yield fecundity estimates that are lower and more variable than estimates from counts of oocytes from mature and ripening females collected at the same time. Based on this conclusion, we discuss methods for developing fecundity estimates in darters. Our results may be broadly applicable to other taxa of fishes with group‐synchronous ovum developmen

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00392.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The reproductive biology of the serranid fishPlectropomus maculatussampled from inshore waters of the Central Great Barrier Reef was studied based on histological analyses of gonad material. This species was shown to be a monandric protogynous hermaphrodite. The process of sex change foliowed the spawning period observed during September through November.Plectropomus: maculatusshowed multiple spawning during this period. Sex change followed the usual protogynous mode with degeneration of ovarian germinal tissue accompanied by proliferation of male germinal tissue in the gonad. The sex structure of the sampled population was analysed based on age and size information. The size and age of first reproduction for females was 30.0cm s. L. and 2 years of age. The size and age of sex‐transition was 35.4 cm s. L. and 4.4 years of age. The sex/size and sex/age relationships indicated that sex‐change can occur over a broad range of sizes and ages. The sizes and age distributions of males and femalesP. maculatesoverlapped over 38% of the length range and over 42% of the maximum age obser

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00393.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Gill structure of rainbow trout and Atlantic salmon was investigated using cell disaggregation and dry fracture techniques for scanning electron microscopy (SEM), allowing new interpreta‐tions of the structure of the secondary lamella. The basement membrane underlying the lamellar epithelium (secondary epithelium) was shown to be a tough sheet with numerous depressions corresponding to underlying pillar cells. This membrane is probably the most important structural element of the secondary lamella, capable of withstanding considerable mechanical stress. For the first time the structure of the apical surface of the secondary lamella was shown by SEM to consist of an outer microridged coat overlying a fibrous coat which appears continuous with the extracellular matrix surrounding the rest of the cell. When cells were detached they rounded up and the external microridged coat became more vesicle like, indicating the labile nature of this coat. In cell suspension preparations, epithelial, mucus and chloride cells are present as well as many blood derived cells such as erythrocytes, presumptive leucocytes and thrombocyte

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00394.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The abundance, the seasonal variation and the life history of the silverside,Atherinomorus lacunosus, are studied from fish caught in the lagoons around New Caledonia. About 270 nights of fishing were carried out between 1980 and 1983. The silverside is present in most of the fishing hauls but seldom in large quantities. Fish reproduce from September to December at 1 year of age. At this time their size is about 10 cm. Mortality is high and a few individuals can survive a second year and reach 13 cm. Results from other studies indicate that in a less seasonally contrasted environment than the lagoons of New Caledonia,A. lacunosushas several spawning periods during the year. This species is thus able to adjust its phenology to the environmental conditions.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00395.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The stomach contents ofOreochromis niloticusfrom L. Chamo were microscopically examined and chemically analysed in order to study the relationship between food quality, growth and condition. More than 20 genera of phytoplankton plus Copepoda, Rotifera and nauplii were present in the stomach contents. The diatom,Melosira, was the most dominant alga in the diet, contributing about 30% of the organic matter. The composition of the food in terms of organic nutrients was dominated by carbohydrate (20.3% dry weight). Both protein and fat made low contributions to the diet; 10% and 5.8% dry weight, respectively. The overall performance of the fish in assimilating food was high: 43.3% for ash free dry weight, 61.2% for protein, 57.2% for lipid, 29% for carbohydrate and 55.7% for energy. The digestible protein‐energy ratio was 15.7 mg kJ−1, suggesting that the food was qualitatively good both for fast growth and for maintaining good condition. It was concluded that the small amount of good quality food ingested, the low fish population density in the lake and the high temperature of the water are the major factors responsible for makingO. niloticusa fast‐growing fish in Lake

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00396.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Seasonal and ontogenetic variations in space and food use byLeuciscus pyrenaicuswere analysed in a Portuguese lowland catchment. Large fish occurred mostly in deep permanent‐flowing sites whereas small fish occurred mostly in the shallowest intermittent‐flowing site. No seasonal or size‐related changes in feeding intensity were found, but the diet changed both across seasons and throughout ontogeny. The diet was dominated by aquatic prey over all seasons, but during winter and summer more plant material and terrestrial prey, respectively, were eaten. Throughout ontogeny fish shifted from soft‐bodied to hard‐shelled prey and decreased animal prey breadth. Mean prey size increased with fish size but the prey size spectrum was more variable for medium‐sized fish than for either small or large fish. It is suggested that: (i) large fish avoid shallow drying areas owing to the risk of mortality, either by thermal and respiratory stresses or increased predation by mammals and birds; (ii) seasonal changes in diet are a response to differences in prey availability; and (iii) morphological constraints, prey handling costs and habitat partitioning are responsible for size‐related ch

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00397.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Ceratomyxa labracisandCeratomyxa diplodae, parasitic in the gall bladder of wild and cultured Mediterranean sea bass (Dicentrarchus labraxL.) were studied. Prevalences were clearly higher in cultured fish, especially for C.labracis. Starvation seems to favour the appearance of ceratomyxosis. Infection varied seasonally, with maxima in winter and minima in summer, a pattern almost contrary to temperature. Prevalence of C.labracisdecreased in older fish. No clear influence of host sex was observed, and the apparent negative association between the twoCeratomyxaspp. was not confirmed statistically. Different degrees of histopathological damage of the gall bladder were observed by light and electron microscopy, mainly consisting of vacuolation, deformation or even necrosis of epithelial cells, and thickening and inflammation of the subepithelial connective tissue. Trophozoites appeared frequently lining the epithelium, closely attached to the cell surface or even forming invaginations in it. The importance of ceratomyxosis for sea bass and the influence of culture and stress conditions are discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Phyletic relations within the haplochromine cichlids of East Africa were investigated using scale and squamation characters. Within the L. Victoria–Edward–Kivu species flock most of the genera proposed in Greenwood's revision could be confirmed by this approach. In addition the genera could be interrelated phylogenetically. They form two distinct superlineages comprising several genera each. The genusAstatotilapiaas conceived by Greenwood is diphyletic. The fluviatile members of the genus form the sister taxon of the L. Victoria–Edward–Kivu flock, while the rest are a subgroup of that flock. The flock seems to be of monophyletic

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Cod were acclimated to 5 and 15° C (cold and warm acclimation, respectively) for at least 43 days after which tissue‐somatic indices, tissue protein, DNA content, and cytochrome c oxidase (CCO) activity were measured. Liver, stomach, intestine, total heart and ventricle‐somatic indices were all increased significantly in the cold acclimated animals compared with their warm acclimated counterparts. There were no differences in gill or white muscle‐somatic indices between the acclimation temperatures. Tissue protein concentration (mg protein g tissue−1) was generally unaffected by temperature acclimation. Cold acclimation resulted in higher white muscle and lower ventricle CCO specific activities(μmol cytochrome c oxidized min−1· g tissue−1) compared with the respective warm acclimated tissues. No significant differences in CCO specific activity were observed in the remaining tissues (when measured at an intermediate temperature of 10° C). Total tissue CCO activity (measured at an intermediate temperature of 10° C) did not differ significantly between the cold and warm

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Mugil cephalusandM. curemacoexist in Tamiahua Lagoon, with no difference in diet or digestive system, but with a separation of 3 months in reproductive timing.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY