A large quantity of urban sewage is drained to a nearby river. Which among the given conditions would happen after mixing of sewage into the river
(i) BOD of receiving water body increases
(ii) DO of receiving water body decreases
(iii) It will not cause mortality among fishes and other aquatic creatures.
(iv) It will lead to nutrient enrichment of receiving water body

Read the following statements carefully and find the incorrect statements: A. More than 1 percent impurities make domestic sewage unfit for human use. B. Less BOD causes mortality of fish and other aquatic creatures. C. Presence of large amounts of nutrients in water also causes excessive growth of planktonic algae, called an algal bloom. D. Algai bloom causes deterioration of the water quality an decreases fish mortality. E. Some bloom-forming algae are extremely toxic to human beings and animals. F. Eichhornia crassipies is the world's most problematic aquatic weed.

Which of the following statements regarding eutrophication are correct ? (i) Eutrophication is the natural ageing of a lake by nutrient enrichment of its water. (ii) Pollutants from human activities like effluents from the industries and homes can radically accelerate the aging process of a lake. This phenomenon is called as cultural or accelerated eutrophication. (iii) The plant nutrients responsible for eutrophication are nitrates and phosphates. (iv) These phosphates and nitrates accelerate the growth of algae, which utilise oxygen and may deoxygenate the water to kill the fish and other aquatic animals.

Give the answer of following questions by observatios from given figures: (i). Which fish has air bladder? (ii) which fish is known as saw fish? (iii) which fish is cartilaginous fish? (iv). Which animal is ectoparasite on true fishes? (v) Which fish has paired fins? (vi) which fishh has body skeleton? (vii) Which fish has 4-pairs of gills? (viii) Whch fis has operculum? (ix) Which fishes are viviparous? (x) Which fish lives in fresh water?