摘要:

The chronology of development ofOreochromis niloticusembryos was examined by scanning electron microscopy (S.E.M.) and the external structures which evolved during the embryonic period were analysed. Twenty‐four stages of embryonic development of this fish at 25°C are described with emphasis on the cleavage phases and morphogenesis of external organs and tissues. Because the development of internal organs could not be observed under S.E.M., the necessary investigation was completed by light microsco

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03347.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The effects of tributyltin (TBT) compounds on gill morphology were examined in the mummichog,Fundulus heteroclitus, in 96‐h LC50 and 6‐week sublethal exposures. Morphometry was used for the identification and quantification of effects with the light microscope. A 96‐h LC50 of 17.2 μg 11was determined. Morphometric analysis of gill tissues revealed hypertrophy of the lamellar epithelium in fish exposed to 17.2 μg 1–1. Relative diffusing capacity was significantly decreased (−41 %); (P<0.05, ANOVA, Bonferronit‐test). At 35.6 μg 1−1, TBT exposure resulted in a significant reduction (− 40%) in the volume of the lamellar blood channels. Both of these observations occurred in fish that showed signs of acute poisoning including loss of equilibrium. In fish exposed to sublethal concentrations of 0.105–2.000 μg TBT 1−1for 6 weeks, there were no pathological changes in the gill. There were no treatment‐related changes in the surface morphology of the gills of fish from both experiments upon scanning electron microscopic examination. Although gill pathology was observed in acutely toxic exposures, it does not appear to be a major

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03348.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Dull coloured, non‐breeding males of the darterEtheostoma flabellare‘freeze’ in response to simulated predatory threat. As they enter breeding condition, colour changes are minor and antipredator behaviour does not change. MaleE. blennioides, which develop bright green colours in the breeding season, also freeze in response to threats in both breeding and non‐breeding states. MaleE. spectabilechange colours dramatically when breeding, developing intense and contrasting orange, blue, yellow and red colours on their sides, fins and throats. In non‐breeding colouration, they freeze when threatened, but in breeding colouration they become less likely to freeze and more likely to flee. These results are discussed both with respect to the hypothesis that changing colours may require changing antipredator behaviour, and in terms of the probable degree of crypticity of these species. Details of the duration of immobility of ‘freezing’ fish and the pattern of subsequent recovery of activity level are a

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03349.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The life‐histories of red roach were assessed in the R. Moros and the R. Ucero, two contrasting tributaries of the R. Duero. Growth occurred from April to October and Ucero red roach were larger than those in the Moros from their second year onwards. Condition increased with gonad development and abruptly decreased after spawning in both populations. The condition of Ucero fish recovered during the summer, but that of the Moros fish remained low. The same year classes (1980 and 1982) dominated both populations. River Moros red roach spawned in a 4‐week period between the end of April and early June, while the spawning season of Ucero red roach lasted until August. The length to fecundity relationship was similar for both populations, and fecundity and ovum size increased with fish length. The life‐history traits of these red roach populations are discussed in relation to current life‐history t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03350.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A new method for measuring maximum stomach or digestive tract volume of fish incorporates air injection at constant pressure with water displacement to measure directly the internal volume of a stomach or analogous structure. The method was tested with coho salmon,Oncorhynchus kisutch(Walbaum), which has a true stomach, and northern squawfish,Ptychocheilus oregonensis(Richardson), which has a modified foregut as a functional analogue. Both species were collected during July‐October 1987 from the Columbia River, U.S.A. Relationships between fish weight (= volume) and maximum volume of the digestive organ were best fitted for coho salmon by an allometric model and for northern squawfish by an exponential model. Least squares regression analysis of individual measurements showed less variability in the volume of coho salmon stomachs (R2= 0.85) than in the total digestive tracts (R2= 0.55) and foreguts (R2= 0.61) of northern squawfish, relative to fish size. Compared to previous methods, the new technique has the advantage of accurately measuring the internal volume of a wide range of digestive organ shapes and size

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03351.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Diets of three scorpaenid fishes,Scorpaena notata, S. porcusandS. scrofa, from aPosidoniaseagrass bed off Marseilles were quantitatively analysed and categorized according to the size and sex of individuals, to elucidate diel and seasonal rhythms. All three preyed on the same crustacean and fish species, but in different proportions:S. notatamostly fed on Caridae,S. porcuson brachyurans andS. scrofaon fishes. Individual size and diel period were the main factors responsible for diet variation and food partitioning that evolved according to both cyclic (temporal) and continuous (ontogenic) trends. A strong interspecific food overlap was observed in juveniles (S.L.<50 mm), whereas intraspecific potential competition was low between juveniles and adults. Among medium and large size classes, intra‐ and interspecific food overlaps were high and of equal intensity. Narrower food niches at night, due to a stronger specialization on type and size of prey, diminished the intra‐ and interspecific potential competition during this period of maximum feeding activity. This probably allowed the high number of coexisting scorpaenid populations in Mediterranean seagrass beds. Nevertheless, microhabitat and time partitioning seemed as important as food partitioning in the structuring of fish assembla

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03352.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The development of the oocytes in the cod,Gadus morhuaL., is described by light and transmission electron microscopy. The oocyte volume increases about 700 times during the stages preceding hydration. The size of the nucleoli increases 35‐fold, the cortical alveoli increase 6‐fold and the yolk granules increase 70‐fold as the oocyte grows. The maximal number of yolk granules is nearly 100000 per oocyte; this number is reduced to less than the half prior to hydration. A significant reduction occurs also in the number of nucleoli at that time. The number of cortical alveoli increases steadily towards hydration. Yolk is deposited in the oocyte as crystalline granules. The lattice is broken down at hydration, leaving the egg transparent. Follicle cells go through a primordial stage and later change to a squamous and to a cuboids shape. The presence of lipid droplets in their interior and the virtual lack of interfollicular spaces are characteristic. The chorion grows to a tripartite structure: an outer thin porous layer, an intermediate homogenous layer and an inner thick helicoidally layer. A mucous substance covers the porous layer. The occurrence of the so‐called lamellae in the helicoidal layer is considered a function of the orientation of its micro fibrils and the plane of sectioning, i.e., not caused by alternating chemical arran

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03353.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Peripheral blood leucocytes were examined for their fine structure and their in vivo response to colloidal carbon particles and bacteria,Aeromonas salmonicida. Four main types of leucocyte were identified: lymphocytes, thrombocytes, monocytes and granulocytes. Previously, two types of granulocyte had been identified but at the electron microscope level a third type could be distinguished in the peripheral blood. Monocytes and the type 1 and type 3 granulocytes were found to be phagocytic.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03354.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Interspecific differences in the stress response of fish may be due, in part, to differences in the sensitivity of target tissues to cortisol. The relative response of brown and rainbow trout to a standardized dose of cortisol was assessed by monitoring condition (K factor), the number of circulating lymphocytes and mortality due to disease, following cortisol treatment. Cortisol implantation resulted in a significant decline in K factor and number of circulating lymphocytes in immature brown trout, but not in immature rainbow trout, despite plasma cortisol levels being similar in both cases. Cortisol implantation in mature brown and rainbow trout significantly increased the mortality rate due to bacterial and fungal infection compared with control fish. Furthermore, the mortality rate due to disease was significantly greater in brown trout than rainbow trout, despite both groups receiving similar doses of steroid.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03355.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

From 475 eels individually marked with floy tags, of which 180 had an additional spot of alcian blue, 142 tags were recovered during a 2‐year release‐recapture programme, but alcian blue spots were not detected. The marked population declined by c. 95% per year (either through death or tag loss); tagged eels did not grow but lost weight; no trap avoidance could be detected. It is concluded that these tagged eels in poor condition did not suffer from winter mortality, and that during summer they moved around very activ

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb03356.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY