Size Selectivity of Active Fishing Gear: Changes in Size, Age and Growth of Cirrhinus Mrigala from the Ganga River, India

Good knowledge of netting approach is essential for scientific and sustainable based fisheries management in lotic water bodies. The large sizes of fishes are more attract to fishers compared to small fishes. This type of fishing is very harmful for future stock and recruitment. 1.5 inch to 3.5 inch mesh size cast net was used in the Ganga River at Allahabad. Cirrhinus mrigala is mainly captured by drag net from the Ganga River, India. Studies were undertaken during March 2014 to February 2015 from the middle stretch of the Ganga River, India. 423 fish specimens (206 males and 217 females) were examined of Cirrhinus mrigala. An over-all picture of age, growth increment and age composition of C. mrigala has been obtained by the study of its scales. The age composition of C. mrigala varied from 0+ to 10+. On the basis of pooled sampled specimen in the total length ranges varied from 16.8 cm to 92.4 cm showed that the fish attained the mean length 30.24 cm, 48.02 cm, 61.50 cm, 70.31, 77.63, 81.84 cm, 85.30 cm, 88.57 cm, 90.15 cm, 91.8 cm in 1+, 2+, 3+, 4+, 5+, 6+, 7+, 8+, 9+ and 10+ age groups respectively. The growth increments in C. mrigala was recorded as 30.24 cm, 17.78 cm, 13.48 cm, 8.81 cm, 7.32 cm, 4.21 cm, 3.46 cm, 3.27 cm, 1.58 cm and 1.65 cm for 1+ to 10+ age groups, respectively. The maximum growth increment was recorded in 1st year and minimum in 9th year of life. The slow growth increment observed after third year may be attributed to the maturity attained after second year of life. It is well known that the growth potential is used for the gonad development. Drag netting is reducing the size of C. mrigala in the Ganga River.