Abstract
Labeo rohita is a member of the Indian major carp species and originally an inhabitant of the Ganga river network in India. It is among the top ten aquaculture species of the world. Since there is a lack of information on the growth pattern of the wild populations of this species, this study aimed at evaluating the pattern of age and growth, to support the development of effective management plans. A total of 1082 samples of L. rohita were obtained from May 2009 to July 2012 in six drainages of the Ganga basin. Scales of the fish were used to determine the age and growth by analyzing the annual rings growth. Out of six populations, a maximum 8+ age classes were recorded from two rivers (Betwa and Sharda). The back-calculated lengths at 8+ age class ranged from 86.22 cm to 91.66 cm. However, for the rest of rivers up to 7+ age classes were recorded. Among growth parameters, specific rate of length increase (C(l)) and specific rate of weight increase (Cw) showed decreasing trend, and three distinct life stages of L. rohita were recorded based on growth constant data (C(lt)). Analysis of variance (ANOVA) of the back-calculated length data set of six populations indicated a significant difference (p < 0.05). All three populations showed significant variation in length attainment during 1+ and 3+ age groups, while two populations showed significant variation in length attainment during the 2+ and 7+ age classes. Additionally, analysis of age frequency at different length intervals indicated that with increase in age class, number of fish samples was reduced. Since the pattern of life history traits of L. rohita have not been attempted in the recent past; therefore, this study will guide fisheries biologists about the current stock structure of this fish across different spatial scale of the Ganga basin.
Highlights
The analysis of life history traits has been widely used by ichthyologists to differentiate among different species and different populations within a species; this method continue to be used successfully (Ihssen et al, 1981)
The focus, which represents the initiation of growth in scales, is located near the anterior field of the scale; while, the larval marks appear in the first year age class and are situated not far from
The present study reported the age and growth composition from six different populations of L. rohita in Ganga basin, and showed considerable intra-basin variations
Summary
The analysis of life history traits has been widely used by ichthyologists to differentiate among different species and different populations within a species; this method continue to be used successfully (Ihssen et al, 1981). Studies on age and growth, maturity of commercially important fishes, provide baseline information that typically assists with the initial recognition and delineation of geographic regions that are representative of individual stocks (Pawson & Jennings, 1996) and is an almost essential prerequisite for successful stock identification (Griffiths, 1997). The use of such parameters is an efficient and cost-effective tool for stock identification, as these data are routinely collected for assessment and management purposes (Ihssen et al, 1981). This study was undertaken to provide information about the important life history attributes (age and growth) of L. rohita, and to compare these aspects among different rivers of the Ganga basin, that may support effective conservation and sustainable management actions for the stocks of L. rohita in the area
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