摘要:

Juvenile salmon, Oncorhynchus tschawytscha Walbaum, were trained to orientate in a direction (270°) and then anaesthetized with ethyl m–aminobenzoate methane sulphonate (MS 222) in a test to determine whether anaesthesia affected the learnt orientation.Before anaesthesia the control group of twelve fish showed a mean unimodal orientation of 264° and a bimodal axis of orientation of 258°/78° with a confidence limit (second order analysis) of 218°←→285°. After administration of MS 222 nine out of ten fish showed marked changes in orientation and random behaviour, persisting in two fish for more than 14 days. The mean of means unimodal orientation, after anaesthesia, was 337° (random) and the bimodal axis of orientation was 337°/157° (random).Eight weeks after completion of the anaesthesia trial the fish were retested. Each fish, except one, showed a mean bimodal axis of orientation that fell within the confidence limit of the control. The mean axis of orientation for ten fish over a 3–day period was 270°/90°, (r) = 0.28.The results support the view that the reference orientation in this study (270°) was a learnt, not an innate directional preference. The effects anaesthesia may have on salmon behaviour during migr

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05349.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Two groups each of approximately 100Moenkhausia dichroua, a schooling characid, showed a long–lasting, constant–oriented swimming when placed in a light–centred circular channel. This apparatus consists of a 1–m diameter circular channel illuminated by either a central or a peripheral light system, so that the light angle is constant all around the channel. With the central light at a fixed angle, fish swam for several months in one direction and reversed direction at a certain date. When the light angle was increased by 10° every other day between 0° (horizontal) and 90° (vertical), swimming direction was reversed at a particular angle in each experiment. This response to artificial light suggests that this small schooling fish uses the sun as an orientation clue in its seasonal

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05350.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The time elvers of the American eel,Anguilla rostrata, spend in an estuary prior to their migration into fresh water was assessed. A distinct mark was formed on elvers' otoliths during their first 2 to 3 weeks in the river estuary. This mark was used to distinguish between growth in fresh water and in salt water. Migrating eels collected at a falls 4 km from the estuary exhibited bimodal length and weight distributions. Frequency distributions showed that eels collected in the estuary were smaller and had smaller otoliths than eels collected at the falls, indicating that elvers do not reach the falls in the same year as they enter the estuary. The three modal groups most probably represent three age–classes. However, the otoliths of elvers collected in the estuary had only the mark of transition whereas eels in the first and second mode at the falls usually had two rings (1–4) and four rings (3–6) per otolith, respectively, in addition to the mark of transition, as viewed under SEM. The possibility that ring formation is not annual means that the use of otoliths for the age determination of eels in this study has not been vali

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05351.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Morphological changes in the oesophageal epitheliumof Oreochromis mossambicus, O. niloticus, andO. mossambicusxO. niloticushybrids were studied during adaptation to sea water. In fresh water, the epithelium is stratified and rich with mucous cells. In salt water, modifications occur in the oesophagus ofO. mossambicusand of the hybrid: mucosa folds are more vascularized and covered with a monolayered epithelium, alternating with a multilayered one. The oesophagus ofO. niloticusdoes not seem to be affected by salinity but this species survives only for brief periods in sea water. These observations underline the close relationship between the oesophagus morphology and salinity tolerance in tilapias.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05352.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Results of experiments on fishes maintained at three different temperatures (25, 30 and 35° C), compared with a control group maintained at 14° C, are presented. Fishes showed obvious signs of stress at 30 and 35° C, as indicated by loss of weight and increase in mortality rate. On the other hand, those at 14 and 25° C gained weight steadily and showed normal growth.Biochemical studies confirm the stress symptoms, as there was a steady, statistically significant fall in blood glucose level and depletion of glycogen reserves in liver and muscle within the first week at 35° C and by the fourth week at 30° C.These results were further confirmed by haematological investigations. All the parameters tested indicated deviation from the normal healthy conditions seen at 14 and 25° C. The deviations in most of the parameters at 35° C were statistically significant from about the second week, and at 30° C by the fourth week. Erythrocytic polycythemia accompanied by an increase in haemoglobin content and haematocrit values were indicative of thermal stress. Leucopenia was mainly contributed by neutrophil decrease, but a relative increase in thrombocytes was recorded.Correlated erythropoietic studies indicated an increase both in the initial (small lymphoid haemoblast) and penultimate (mature reticulocyte) stages in red cell development, although the intermediate stages decreased in number. Similar trends in the different stages of neutrophil development were observed. The significance of these changes in the context of homeostatic phenomena is d

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05353.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A survey based on monthly sampling of commercial catches was carried out in the Cross River estuary in 1984 and 1985 to determine the extent of parasitization and occurrence of externally visible lesions on the bagrid catfishChrysichthys nigrodigitatus.Infections with the following parasites were encountered:Henneguya chrysichthyi(32%),Protancylodiscoides chrysichlhes(77%).Siphodera ghanensis(4.2%),Aspidogaster africanus(0.1%),Hysterothylaciumlarvae (64%),Nerolica orbignyi(1.5%),Ergasilus lalus(27%), andChonopeltis brevis(0.02%). A new kind of epidermal papilloma was found and is described. On a yearly average, less than 0.5% of the catfish population was affected by either skeletal deformities or skin ulceration. Fin rot was observed from December to May, reaching a prevalence of 79% in February. Gill myxozoosis due toHemwguya chrysichthyiis considered the most important parasitic disease of the fish, occurring throughout the year with a maximum prevalence of 76% in October. Results of the study are discussed in the light of a projected intensive cultivation of the fish in the extensive estuaries and lagoons bordering Nigeria's coastline.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05354.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Populations of aerobic heterotrophic bacteria, occurring on the gills of healthy turbot, were estimated using a dilution plate technique. From a comparison of 18 media, the highest counts, i.e. 7.0 × l05g−1, were obtained after incubation at 15–25°C on a specifically formulated medium which contained low quantities of beef extract, casein, tryptone and yeast extract. These bacteria were equated withAsticacaulissp.,Hyphomicrobiumsp.,Janthinobacterium lividum, Prosthecomicrobiumsp.,Pseudomonas fluorescensandVibriosp. Evidence from scanning electron microscopy pointed to a general lack of intimate colonization of exposed areas of the gill. Instead, micro‐organisms colonized protected niches, such as the clefts between lamellae and in secluded areas on the

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05355.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Serrasalmids of the genusMylossomaare obligate gill‐breathers that are encountered in the floodplain lakes of Amazonia, even when the oxygen concentrations there are below 0.5 mg l−1. It was shown by experiments that fish of these species are capable of utilizing the oxygen‐rich surface layer of the water for respiration, in order to survive periods of habitat‐induced hypoxia. This so‐called aquatic surface respiration entails an increase in locomotory activity and an ecomorphosis involving the formation of a dermal extension on the lower jaw, that apparently has a hydrodynamic function for using the surface layer for gill respiration; when the water is aerated, it retrogresses to its original size. Histological examination showed that the extension is formed by edematous processes in the stratum s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05356.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

This study describes a pattern of circulus spacing on the scales of sockeye salmon,Oncorhynchus nerka, which has not been reported previously. The average distance between circuli formed during the second year of ocean growth is much less than that of first year or in subsequent years. This pattern was persistent for fishes of two river systems, six year–classes and two age groups (2.2 and 2.3) and was due to summer growth. Statistical analyses were conducted only on age 2.2 fish because of small sample sizes in four of the six years for age 2.3 fish. There were significant (p<0.05) differences in the distance between circuli formed in the summer and in the two stocks for various years at sea. No significant variation in average spacing between circuli was explained by oceanic temperatures.Annuli were formed between November and January. However, oceanic temperatures were declining at this time and do not reach minima until April. Thus, annuli are formed about the time of the equinox and during a declining temperature regime. We hypothesize that the pattern of circuli spacing and annulus formation are responses to photoperiod and food availability which the fish experience during their existence at se

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05357.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Thein vitroeffects of gases and temperature on the osmotic fragility of carp erythrocytes were studied. At the three different temperatures analyzed (5, 11 and 20°C) there was no noticeable modification in erythrocyte membrane osmotic resistance. Osmotic fragility of red blood cells was altered by CO2and air treatment, as compared to the standard procedure. This suggests the need to take into account a possible moderate hypoxia that develops in the routine procedure of nucleated erythrocyte osmotic fragility tests

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05358.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY