MORPHOMETRIC STUDY OF THE MUD EEL MONOPTERUS CUCHIA (HAM.) FROM THE NEW ALLUVIAL ZONE OF WEST BENGAL

Monopterus cuchia, commonly known as Gangetic mud eel, is a fish with snake like appearance and smooth slimy skin. The eel belongs to the family Synbranchidae and order Synbranchiformes. It is an indigenous fish species of the New Alluvial Zone of West Bengal, locally known as 'Cuche'. The natural habitat of the fish is rivers, ponds, beels and other freshwater bodies. The eel is rich in protein, iron and vitamin content and quite relished as a food fish by the economically backward people and tribals of West Bengal. The fish population has dwindled to a considerable extent in the New Alluvial Zone of West Bengal due to urbanisation, intensive agriculture and above all population explosion. This fish has been determined to be an endangered fish (Das and De, 2002).


INTRODUCTION
Monopterus cuchia, commonly known as Gangetic mud eel, is a fish with snake like appearance and smooth slimy skin.The eel belongs to the family Synbranchidae and order Synbranchiformes.
It is an indigenous fish species of the New Alluvial Zone of West Bengal, locally known as 'Cuche'.
The natural habitat of the fish is rivers, ponds, beels and other freshwater bodies.The eel is rich in protein, iron and vitamin content and quite relished as a food fish by the economically backward people and tribals of West Bengal.The fish population has dwindled to a considerable extent in the New Alluvial Zone of West Bengal due to urbanisation, intensive agriculture and above all population explosion.This fish has been determined to be an endangered fish (Das and De, 2002).
Though the biological study of other food fishes like Indian Major Carps have been done by several workers, the study on M. cuchia is very few.No work has been done from West Bengal.Thus, the present study was undertaken to study the biology of Monopterus cuchia from the New Alluvial Zone of West Bengal and this paper deals with the morphometry of M. cuchia from the New Alluvial Zone of West Bengal.This kind of study is very much essential for solving the race problem, Zupanovic (1968) stated "As it is essential to distinguish between different species, so it is essential to distinguish between the self perpetuating sub-groups within the species.These subgroups may be equivalent to what taxonomists call sub-species, but they may be equivalent to what taxonomists call sub-species, but they may be generally of lesser rank, in the fishery literature, they are often called races or populations."

MATERIALS AND METHODS
The material for the present study pertains to the specimens of Monopterus cuchia collected from various beels of the New Alluvial Zone of West Bengal (21.5-24.5°North Latitude and 86-89° East Longitude) during the period February 2005 through January 2006.Specimens were collected every month and immediately after collection specimens were fixed in 10% formalin and brought to the laboratory for detailed measurements.The study is based on the examination of 62 specimens in the size range of 15.0 to 80.5 cm.A total of 12 morphometric parameters (Fig. 1) have been taken up for study according to the methods described by Lowe-McConnel (1976).
Divider and measuring board, having graduations in centimeter have been used for various measurements.All linear measurements were made to nearest centimeter.
The number of times each morphometric character went into reference length of the fish was considered as Biometric Index (Tobor, 1974).For each character, a mean biometric index for each 10 cm length group has been calculated.
The regression of various morphometric characters on total length was obtained by least square method with the formula : where 'Y' is the variable character such as head length, body depth etc., '0' is the constant value to be determined, 'b' is the regression co-efficient and 'x' is the total length.The correlation coefficient 'r' of these regressions was computed.

RESULTS AND DISCUSSION
The mean and range of various morphometric characters of M. cuchio has been presented in Table 1.The morphometric characters showed a positive increase with increase in length of the fish.The regression equation of different variable characters (Y) on total length/ head length (X) has been presented in Table 2.The regression co-efficient' b' of different variable characters indicates that the rate of growth in respect to total length is highest in case of head width and lowest in case of pre-orbital length in relation to head length.High values of correlation co-efficient 'r' (Table 2) obtained indicates a high degree of positive correlation between the different morphometric parameters with the reference length (Total length/ Head length).Biometric index of M. cuchio (Fig. 2) studied indicates that the indices of length of caudal peduncle, gapa of mouth, and inter-orbital length were almost constant.According to Bayagbona (1963), a constant index in any of the biometric characters in relation to its reference length is isometric.The indices of the growth of head depth and body depth in relation to total length and upper jaw length in relation to head length was found to be allometric.
The mean and range of different morphometric characters of males and females of M. cuchio has been presented in Table 3. Considerable difference in the morphometric characters has been observed between males and females in their head regions.The males were found to have greater pre-orbital length.On the other hand the females had greater gape of mouth.According to   Inter orbital depth (100) 1.0 0.8-1.21.02 0.9-1.3 Head width (HW) 2.7 2.0-3.5 2.52 1.9-3.0Gold (1966) ratios between morphological characters of fish will not necessarily be constant for the organisms of the same species due to variation resulting from differences in sex, race and nutrition and/or other environmental factors.
In the present study an attempt has been made to compare the morphometric characters between dark and white varieties of M. cuchio.Variations have been observed between various characters (Table 4).Percentage of length of caudal peduncle, head length, post-orbital length and body depth in relation to total length was found to be higher in white varieties.Such variations are also evident from the regression equations (Table 5).From the 'r' values of the different parameters it is clear that the different parameters in case of dark variety are more correlated with their reference length in comparison to the white variety.
The biometric indices (Table 6) shows that the growth of length of caudal peduncle in relation to total length is isometric in both varieties and the growth of inter-orbital length in relation to head length is isometric in both the varieties.The growth of gape of mouth in relation to head length is isometric in the dark variety and head length in relation to total length is isometric in the white variety.All the other characters are allometric in both the varieties.
10hal et oZ., (1994) classified various morphometric characters on the basis of range difference into genetical (less than 10%), intermediate (10-15%) and environmentally (greater than 15%) controlled characters.In the present study head width, post -orbital length, head depth and body depth where range difference is greater than 10% can be considered as genetical characters.Head length, where range difference is 10-15% can be considered as intermediate character and length of caudal peduncle, pre-orbital length, upper jaw length, lower jaw length, gape of mouth and inter-orbital length where range difference is greater than 15% can be considered as environmentally controlled characters according to the classification given by 10hal et oZ., (1994). 10hal et oZ., (1994) reported 13 characters in relation to total length to be genetically controlled in Tor putitora.Bhatt et oZ., (1998) reported 11 characters in relation to total length to be genetically controlled in the same species.This knowledge is important since Vladycov (1934) maintains that in the fish species showing restricted distribution, the majority of morphometric characters show narrow range

Table 1 .
: Morphometric analysis of Monopterus cuchia from the New Alluvial Zone of West Bengal (Jungle beel).

Table 5 .
: Regression equations of morphometric parameters of M. cuchia (Black and White variety).

Table 6 .
: Biometric index of M. cuchia in different length groups (Black and White variety).