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The effect of emersion and handling on the nitrogen excretion rates of Clarias gariepinus 总被引:1,自引:0,他引:1
African catfish Clarias gariepinus (=119.9&30.6 g) were exposed to periods of emersion (5, 30, 60, 90 and 180 min) and the ammonia and nitrogen excretion rates measured following re-immersion. Immediately following re-immersion (0–30 min), the ammonia excretion and relative ammonia excretion was greatest for the 5-min emersion gro up. Exposure to extended periods of emersion resulted in a decrease in total nitrogen excretion, notably ammonia excretion, although no significant changes were observed in the non-ammonia component of C. gariepinus . 相似文献
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AV Shevchenko IG Budzanivska TP Shevchenko VP Polischuk D Spaar 《Archives Of Phytopathology And Plant Protection》2013,46(2):139-146
The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants. 相似文献
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The fish fauna of the newly inundated Lake Itezhi-tezhi, Zambia was observed between 1980 and 1985. Marked changes in the community structure were identified. The most obvious were a decline in species diversity and a shift in species composition from acommunity with a preponderance of Alesles lateralis (Boulenger) (Characidae), to one dominated by cichlids. These changes were primarily due to members of the families Cyprinidae, Mormyridae and Schilbeidae being unable to adapt to the new environmental conditions, such as spawning and feeding grounds, and their inability to cope with fluctuating water levels in the lake. It was suggested that a sound fishery data collection system be implemented to provide reliable information on which to base management policy. 相似文献
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Observations on the ecology of a landlocked population of allis shad in Aguieira Reservoir, Portugal
M. J. Collares-Pereira ‡ I. G. Cowx † T. Sales Luís N. Pedrosa M. Santos-Reis 《Journal of fish biology》1999,55(3):658-664
A landlocked population of the anadromous clupeid Alosa alosa from Aguieira Reservoir in Portugal is described. The individuals are fast-growing, mature in their third year of life, live for 5+ years, and consequently spawn more than once. 相似文献
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M. Njiru J. E. Ojuok J. B. Okeyo-Owuor M. Muchiri M. J. Ntiba I. G. Cowx 《African Journal of Ecology》2006,44(1):30-37
The life history characteristics of introduced Nile tilapia (Oreochromis niloticus L.) in Lake Victoria, including, sex ratio, fecundity, reproduction, weight‐length relationship and body condition were studied and compared with those of other populations. Samples were collected by trawling and seining in the Kenyan sector of Lake Victoria between June 1998 and December 2000. Males predominated over females (sex ratio 1.42 : 1 : 00). O. niloticus spawned throughout the year but with a peak between December and June. Length at first maturity was (mean ± SD) 30.81 ± 0.09 for females and 34.5 ± 6 0.48 for males. There was little seasonal variation in relative condition, which ranged from 0.92 to 1.05 in males and 0.94 to 1.07 in females. Gonadosomatic index (GSI) was low during the postspawning period (July to October) and high during the protracted breeding period (December and June). Fecundity ranged from 905 to 7619 oocytes for fish of 28 to 51 cm total length (TL) respectively. The relationships between fecundity (F) and total length (L), weight (W) and ovary weight (OW) were: F = 8.159L1.53, F = 96.269W0.4504, F = 1806 + 39.4OW. The slope b of the weight‐length relationship was 3.08–3.32 for males and 3.07–3.22 for females. Growth was allometric in both cases and was significantly different from the expected value of 3. The life history strategy of O. niloticus is discussed in context of environmental changes occurring in the lake. 相似文献
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Aquatic predators and habitat permanence can jointly affect benthic invertebrate biomass and community composition. In 2006
I sampled fish and invertebrates in ten ponds embedded in a seasonal wetland before and after a natural drought. Drought reduced
fish biomass and density leaving some ponds in a fishless condition when rains returned in July. In July, large aquatic insects
and crayfish colonized and reproduced in the ponds, but did not colonize all of the ponds equally. Using measurements of fish
abundance and other environmental parameters of the ponds, I conducted linear regression analyses to explore potential drivers
of variable invertebrate biomass in July. Fish biomass had a negative effect on invertebrate biomass and it explained more
of the variation in total invertebrate biomass and total non-shrimp biomass than fish abundance (number of fish caught). Dissolved
oxygen and pond depth were both correlated with fish biomass, but were poorer predictors of invertebrate biomass. Ponds with
few or no fish had 20× greater total biomass and 200× more non-shrimp biomass than ponds with high fish biomass. Shrimp dominated
the invertebrate composition, and were only found in the two deepest ponds with the highest fish biomass; predatory insects
and crayfish dominated the other eight ponds. When taxa were analyzed separately, fish biomass explained a large portion of
the variation for predatory insects (Coleoptera, Hemiptera, and Odonata) and crayfish (Procambarus alleni), but dissolved oxygen was the best predictor of larval stratiomyid (order Diptera) biomass. These results are generally
consistent with studies demonstrating negative effects of fish on large predatory invertebrates, but also suggest that more
severe local droughts can seasonally enhance insect and crayfish populations by generating fishless or nearly fishless conditions.
Handling editor: J. Trexler 相似文献
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Retention and mortality associated with visible implant elastomer (VIE) and passive integrated transponder (PIT) tagged juvenile chub [ Leuciscus cephalus (L.)], dace [ Leuciscus leuciscus (L.)] and roach [ Rutilus rutilus (L.)] were evaluated. PIT tag retention (96.6–100%) was higher than VIE over the 6-month duration of the experiment. VIE retention was significantly better in the head (96.3–98.8%) than in the fins (78.8–90.9%) the first month after tagging, but the opposite was found after 6 months (head = 21.5–57.5%; fins = 77.2–88.8%). Survival was not significantly different from controls for any treatment, except dace tagged with 23-mm PIT (significantly influenced by mass of fish at tagging) and sham PIT tagged dace, because of initial losses. PIT tags are recommended as the most suitable method for tagging individual juvenile chub, dace and roach based on high retention and survival. VIE implantation in the head (studies < 30 days) and fins (studies > 30 days) could provide a cheap, batch-marking alternative, provided retention rates are monitored. 相似文献
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The winter diets of 0+ year juvenile dace Leuciscus leuciscus and roach Rutilus rutilus in the lower River Trent, England, were dominated by aufwuchs. There were no significant changes in the relative condition of either fish species over the winter. 相似文献