摘要:

The spawning season of chub,Leuciscus cephalus, in western Greece starts in January‐February when males are aged at least 2 + and females 3 + (rarely 2 +) years. In the R. Ermitsa (Achelos R. basin) a population is reported with fingerling adult males with developed gonads and breeding tubercles at a size of 42 72 mms.l.Leuciscus pleurobipunctatusbreeds between February and the first half of May, when males are aged at least 1 + and females 2 + (sometimes also 1 +); their life span is about 4 years. L.cephalus × L. pleurobipunctatushybrids were found in the R. Ermitsa (five specimens) and R. Louros (one specimen). In the former the contemporary presence of adult fingerling male chub, the smallest adults of L.pleurobipunctatus, and hybrids between the two species, may be related to channel width and the human interference which has resulted in considerable disturbance of the habit

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05331.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Laboratory experiments measuring survival and growth at various pH levels and two temperatures indicate that the threshold of pH of water below which larval development of carp is stopped is 5.0–5.2, the development of some individuals being stopped within the pH range 5.0–5.5. Inhibition of development is due to the inability of a larva to fill its swimbladder with air, this preventing swimming and leading to death from starvation. In water of pH 5.5–6.0 the development may be undisturbed, though slower. The effect of water acidification is reflected in slower growth rate and prolongation of the larval stages of develo

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05332.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The emergence timing, quality and diet of chinook salmon,Oncorhynchus tshawytscha, fry were studied as they emerged from ten natural redds. The impact of selected environmental factors on emergence was studied also. Samples of fry were obtained daily using redd traps.The mean period of total emergence for redds with more than 450 fry emerging was 44.8 days (range 25–57 days), but for 80% of the fry in each redd to emerge the mean time elapsed was 10.8 days (range 6–21 days). No fry sampled had a visible yolk sac. The effect of temperature and light on emergence timing was weak, but stream flow had a strong influence. Fry length was constant for each redd throughout emergence, but fry weight tended to decline; consequently condition factor declined also. There was evidence that fry fed before emergence, but they did not grow. The major prey item,Deleatidiumspp. (47.4% of the contents of all stomachs sampled), was the most abundant invertebrate in stream benthos and drift. Empty stomachs were prevalent at the start of emergence, with full stomachs becoming more common as emergence progressed.The time distribution of numbers of fry emerging was usually unimodal, but occasionally bimodal. Over one third of fry emerged during the best 2 days of sampl

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05333.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Although sympatric populations of sticklebacks occur commonly along the north‐eastern coast of North America, very few studies have considered the interspecific relationships within such populations. This paper investigates prey selectivity, feeding behaviour and potential prey availability within sympatric populations from five brackish‐water sites in New Brunswick. Differences between the diets of species from different sites were related to differences in the range of prey available. Fish collected from sites with abundant aquatic vegetation consumed greater numbers of prey than those from vegetation‐poor sites. The proportions of prey types eaten by both adults and juveniles reflected prey species abundance at the different sites; thus shifts in diet over time were found to be related to changes in the abundance of potential prey and not to shifts in prey preference on the part of the fish. The size of prey consumed was related to mouth size; adult and juvenileGasterosteus wheatlandi, having the smallest mouths, consumed the smallest prey. Differences in prey size detected in the four species studied were due to differences in the types of prey consumed. Laboratory experiments on feeding behaviour showed that adultApeltes quadracusandPungitius pungitiuswere more efficient at capturing benthic prey than wereGasterosteus aculeatusandG. wheatlandi.Competition for food is thought not to occur in these populations, because of the abundance of potential prey and the morphological constraints on feeding beha

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05334.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Softwater (Ca2+=50, Na+= 50(μequiv. l−1) acclimated rainbow trout were fitted with chronic arterial catheters to allow for repetitive blood sampling. After 48 h recovery they were then exposed to either control (pH 6.5, Al = 0μg l−1), acid (pH 4.8, Al = 0μg l−1) or acid plus aluminum (pH 4.8, A1 = 112 μg l−1) conditions for 72 h. Parameters measured included blood glucose, lactate, haemoglobin, haematocrit and plasma Na+, Cl−, protein and cortisol.Exposure to pH 4′8 alone caused no mortality, a moderate ionoregulatory disturbance and a transient elevation in plasma cortisol. All other parameters were not significantly different from controls. Addition of aluminum to this exposure caused 100% mortality with a mean survival time of only 27.0 h. There was a marked decrease in plasma ions, hyperglycemia, lactate accumulation, haemoconcentration, red cell swelling, and a sharp rise in plasma cortisol becoming greatly increased as the fish neared death. The mechanism of toxicity of acute acid/aluminum exposure, the role for cortisol under such conditions, and the validity of cortisol and glucose as indicators of stress in fis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05335.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In a reared population of individually marked juvenile masu salmon, individual growth was monitored from the first autumn in 1983 to the following spring. The potential smolts were not significantly greater in mean fork length and body weight than the potential parr in late August of the first year, but they then grew faster until March of the second year. As a result, the potential smolts formed the upper mode of the bimodal length distribution after February. Especially in autumn (October and November) the specific growth rates of potential smolts were significantly greater than those of parr, and the bimodality in growth rate distribution was more distinct for males than females. These suggest that there are two groups having different growth rates in autumn of the first year and that sufficient growth in this period may play an important role in smoltification in the following spring.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05336.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AdultBagrus docmacin the Nyanza Gulf of Lake Victoria feeds mostly on fish–Haplochromisspp. andEngraulicypris argenteus(Pelligrin). Juveniles prefer aquatic benthic invertebrates withPhyllogomphus aethiop.?(K.elys),Phanostoma senegalense(Brauer), Chironomusspp. andCaridina nilotica(Roux) dominating, followed byChaoborusspp.,Povilla adusla(Navas),Valvataspp. andNeoperla spio(Newman) in order of importance.B. docmacexhibits diurnal changes in feeding habits. It feeds actively during dusk and dawn, taking advantage of the twilight environment for successful feeding mission–a crespuscular feeding behaviour. Selectivity of food seems dependent on occurrence of prey items. The species has an ubiquitous distribution in the Gulf but occurs more frequently with increasing water depth and decreasing water temperature. The biomass of the predator shows little correlation with water conductivity.Bagrus docmacand the other important piscivorous species in the lake,Lates niloticus(L.), are mutually exclusive in their bathymetric distribution within the Gulf. They also have different preferences for water temperature and conductiv

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05337.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Examination of juveniles (25–50 mmt.l.) of the three species of grey mullet present in British and other nothern European waters has indicated that the melanophore pattern on the ventral surface of the head is a reliable and useful character for identificatio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05338.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Loch Fleet is an oligotrophic upland lake in Galloway, south‐west Scotland. It once supported a brown trout,Salmo truttaL., sport fishery with low annual catches (<150 fish year−1) but catches declined markedly after 1950 and no fish were caught after 1975. Diatom records for the lake sediments indicate acute acidification since 1975, pH changing from c. 5–8 to 4–6.In 1984 a project was set up at Loch Fleet to investigate techniques of acidity mitigation, with a view to restoring fisheries in this and similarly affected waters. An underlying assumption of the project was that fish had been lost as a direct result of acidity and associated factors. Studies were therefore undertaken during a 2‐year baseline period (1984–1986) to validate this assumption.Fish surveys using a variety of techniques (gill‐netting, trapping, electrofishing) confirmed that trout were absent from the Loch and its afferent streams, and also from its main outlet stream, the Little Water of Fleet, for a distance of 7 km downstream. Trout were present below this point but are prevented from passing upstream by a 5‐m waterfall. Eels,Anguilla anguillaL., were present throughout the Little Water of Fleet, though not in the Loch itself. Population densities of both species were low, with less than 7 eels and 5 trout per 100 m2.Survival studies using brown trout ova and yolk‐sac fry indicated that conditions in the Loch and its afferent streams were acutely toxic to these stages as a result of the low pH (pH 4.5), low calcium (I mg l−1) and high aluminium concentrations (200 μg 1−1total Al, 60 μg 1−1inorganic monomeric Al). Trout fingerlings could survive these conditions in short‐term tests (9 days) but, in chronic exposure tests lasting up to 180 days carried outin situin streams adjoining the loch, no fish survived this period. This toxicity was eliminated in experiments where pH was raised to 5.4 by KOH addition.It is concluded that the loss of the brown trout fishery at Loch Fleet occurred as a direct result of acidity and related factors, probably acting in the first instance on the sensitive intra‐gravel ova and yolk‐sac fry stages,

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05339.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The bimodally respiring catfishClarias macrocephalusGünther responded to a toxic extract ofCroton tiglium(Euphorbiaceae) seeds by increased air breathing under both normoxic (8.1 ± 0.4 mgO2l−1) and hypoxic (0.7 ± 0.1 mgO2l−1) conditions. Fish in hypoxia survived longer than those in normoxia when surface access was provided. When air breathing was prevented, survival time in toxin was greatly reduced at both levels of dissolved oxygen, and fish in normoxia survived longer than those in hypoxia. Non‐toxin controls without surface access survived in normoxia but in hypoxia died at the same time as the fish in toxin. These results suggest that air breathing increases the resistance offish to toxins by permitting a decrease in the rate of gill ventilation and hence the rate at which toxins are

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05340.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY