Interrelationship between physico-chemical characteristics of a tropical lake and their impact on biodiversity of planktons.

The physicochemical parameters including temperature, pH, dissolved O2, free CO2, total alkalinity, permanent hardness, salinity, transparency, specific conductivity, BOD, COD, phosphate and nitrate were studied in a tropical lake, called Bonhooghly Lake (situated at Baranagar, Kolkata) around the year 2014 and the correlation between the said parameters, as well as their impact on Biodiversity indices were made. There is stable increase of CO2 content in water from August (27.24 mg l-1) and afterwards due to decaying of plant materials. Therefore there is a slight fall of pH (7.1). Significant negative correlation (p<0.01) between pH and CO2 content was also obtained. It also shows a significant negative correlation with O2 content as well. During February and March transparency of water falls significantly with the increase of algal bloom. It significantly decreases dissolved O2 content and pH but increases free dissolved CO2 (p<0.01). Phosphate has a definite correlation with nitrate content of the Lake, possibly because both are among the most essential nutrients of living system. Increase of one obviously indicates escalation of other. During the early months of the year phosphate and nitrate content of water increased steadily (up to 0.13 and 1.85 mg l-1 respectively) and a very high number of Chlamydomonas(up to15100 l-1) and Chlorella (up to 13140 l-1)were observed. Species richness indices (Menhinick's index) of Phytoplanktons were observed maximum in the month of May, dominance (Simpson's index) in January and diversity (Shannon-Weaver index) in April. Zooplanktons also followed the same trend indicating close interdependence. It was significant that apart from other factors, temperature played a most pivotal role in bringing the diversity in the plankton community.

Responses of succinate dehydrogenase and non-specific alkaline phosphatases and mortality of tilapia to ambient pH stress in a sewage-fed aquaculture pond.

The fish, tilapia (Oreochromis mossambicus) of 50-60 g body weight was experimentally exposed to effluent gradients of highly alkaline pH in a sewage-fed aquaculture farm for examining the pH stress-induced responses of mortality and the stress marker enzyme succinate dehydrogenase and the non-specific alkaline phosphatases of fish prior to death at different hours of intoxication. A second trial was performed after two months when water quality changed along the sewage effluent gradient. An in situ experiment was also performed for better understanding of the responses of enzymatic activities attributable to different levels of pH conditions. Time required for 100% mortality of fish tended to increase from 30 min in pH 11.6 to 22 hr in pH 10.2. There was no mortality of fish when water quality improved significantly (with pH ranging between 9.6 to 8.0) after two months. The activities of succinate dehydrogenase and intracellular alkaline phosphatases assayed in gills and liver prior to death of fish tended to reduce with increase in survival hour, following a pattern of decay curve. On the other hand, percent of enzymatic inhibition of the exposed fish over the control increased as the survival hour increased following a pattern of exponential curve. It appears that the highest water pH of 11.6. maximum ratio for ammonium to ammonium hydroxide (1: 21) and reduced level of dissolved oxygen (2.62 mg/l) were perhaps responsible for the 100% mortality of fish within 30 min of their exposure and the enzymatic activities in the gills and liver assayed prior to death of fish tended to reduce as the acclimatization period of fish increased and vice-versa.