The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983-I984 Esox lucius. PercaJluviarilis. Ruiilus rutilus, Scardinius eryrhrophthalmur, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH25) Rutilus rutilus. Scardinius erythrophthalmus. Perca puviatilis, Icialurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra p.vgmaea was extremely acid-tolerant. The percentage of waters which harboured fish as well as the average number of fish species per water decreased steeply between pH 6 and 4.The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification. six groups ofwaterscould be distinquished with respect to their fish fauna. The site groups are defined and characterized physico-chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the Occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.
Sensitivity o f eggs and sac fry of the com mon carp {Cyprinus carpio) to pH levels in th e range o f 4.5 to 7.5 was assessed up to 117 h after fertilization. Studied param eters were rate o f em bryonic development, time and duration of hatching, and spinal cord deformation. In the pH range between 4.75 and 5.2 egg mortality was highest and a delay in the rate o f embryonic development and hatching was observed in the surviving embryos. A strong increase of spinal cord deform ation o f sac fry occurred in the lo w er pH ranges (pH 5.5-4.75). Common carp appeared to be more sensitive to acid stress than m an y other species of fish.
The acute and chronic toxicity of chloroform has been studied in laboratory animals. An acute oral LD50 of 2.0 (1.0-3.8) g/kg was determined for male rats. When applied to the skin of rabbits, chloroform produced slight to moderate irritation and delayed healing of abraded sking. Absorption of chloroform through the skin of rabbits was apparent but absorption is not expected to present a practical acute hazard. Liquid chloroform produced slight injury to the eyes of rabbits which took over a week to heal. Repeated 1-hour exposures five days per week for six months to either 85.50 or 25 ppm of the vapor of chloroform resulted in adverse effects in all or some species studied: rats, rabbits, guinea pigs and dogs. The effects at 25 ppm were slight and reversible. Rats exposed to 25 ppm for 4.2 or 1 hour/day for 6 months were not adversely affected. Based on experimental data and published reports on human experience as well as industrial experience with carbon tetrachloride, the authors suggest that when worker's exposures can be expected to be repeated and prolonged, the exposure concentrations be maintained below 25 ppm vapor and that the time weighted average not exceed 10 ppm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.