
Research Article


Lengthweight Relationship of Mugil cephalus (Linnaeus 1758) in
Vellar Estuary, Southeast coast of India 

S. Murugan,
S. Ajmal Khan,
P.S. Lyla,
C. Prasanna Kumar,
K.C.A. Jalal,
B.Y. Kamaruzzaman
and
B. Akbar John



ABSTRACT

A detailed study on the length weight relationship of Mugil
cephalus in Vellar estuary was conducted between January 2004 and December
2005. Statistical tests such as regression coefficient ‘b’
and ‘a’
tests were performed to compare the b values of males and females from the hypothetical
value of 3. The b value of male (2.7658) differed significantly from the hypothetical
value of 3 (t = 2.8586<0.05), the b value of female (2.8586) did not differ
significantly from the hypothetical value (t = 1.0158>0.05). Values of both
males and females were less than 3 which proved the negative allometry growth
pattern.




How
to cite this article:
S. Murugan, S. Ajmal Khan, P.S. Lyla, C. Prasanna Kumar, K.C.A. Jalal, B.Y. Kamaruzzaman and B. Akbar John, 2012. Lengthweight Relationship of Mugil cephalus (Linnaeus 1758) in
Vellar Estuary, Southeast coast of India. Pakistan Journal of Biological Sciences, 15: 595599. DOI: 10.3923/pjbs.2012.595.599 URL: https://scialert.net/abstract/?doi=pjbs.2012.595.599



Received: October 01, 2012;
Accepted: October 04, 2012;
Published: January 23, 2013


INTRODUCTION
Lengthweight relationship is considered vital in fisheries as it correlates
and reveals the mathematical relationship between the variables length and weight
of the fishes (Lawson, 2011; Arshad
et al., 2012; Thulasitha and Sivashanthini, 2012).
Studies on lengthweight relationship play a vital role in predicting the growth
rate, feeding intensity, metamorphosis and general well being of the fish population
(Sivashanthini et al., 2009; Hazmadi
et al., 2011). Besides comparing the life history of fishes of different
localities (Petrakis and Stergiou, 1995), the lengthweight
relationship can also be used for estimating the number of fish landed and comparing
the population in space and time (Cicek et al., 2008;
Khan et al., 2011). Knowledge of the relationship
between the weight of a fish and its length is also helpful to biologists in
converting samples of length frequency data into weight data for calculation
of catch in terms of weight or biomass. The lengthweight relationships could
also be used to (1) estimation of mean weight of the fish of a given length
group (Beyer, 1987); (2) conversion of lengthgrowth
to weightgrowth equivalents in yield per catch and related models, (3) interspecific
and inter population morphometric comparison of fish species and (4) assessing
the wellbeing of fish population (Bolger and Connolly,
1989; Kulbicki et al., 1993; King,
1996a; Hajjej et al., 2011). In tropical
waters, the fish growth fluctuation is more frequent due to seasonal variations,
more spawning and composition of food (Das et al.,
1997; Amin, 2001). Venkataramanujam
and Ramanathan (1994) were not having a different opinion pointed out that
it is the direct way of transforming logarithmic growth rates into weight and
the same shows major taxonomic variations and incidences in the life history
like metamorphosis and the onset of maturity. Lengthweight relationship is
helpful in the evaluation of the condition or general well being of the animal
through the study of condition factor (K) or relative condition factor (KN).
It is worth mentioning that virtually no information on the lengthweight relationship
of Mugil cephalus from Parangipettai waters are available. Therefore
the present study was undertaken on the lengthweight relationship and relative
condition of Mugil cephalus occurring in Vellar estuary.
MATERIALS AND METHODS
Description of the study area: Parangipettai (lat. 11°30’N,
long. 79°46’E) situated on the southeast coast of India in endowed
with a variety of biotopes such as neritic, estuarine, backwater and mangrove
swamps within easy reach of our biological station. The Vellar River has its
origin in the Servarayan hills in Selam district, 240 km west of Parangipettai.
It opens in to the Bay of Bengal at Parangipettai after flowing over a distance
of about 480 km. This estuary is 600 m wide at its junction with the sea. This
is a true estuary and is subjected to long term seasonal variations in salinity.
During the northeast monsoon (October to December) the estuary drains more of
fresh water.
Data collection: Mugil cephalus were collected from the commercial
catches brought to the fish landing centers of Parangipettai for the period
of two years from January 2004 to December 2005. A total of 840 specimens (390
males and 450 females) ranging in size from 10 to 49 cm for males and 10 to
54 cm for females were used for the present study . The Total Length (TL) of
each fish was measured from the anterior most edge of the snout to the posterior
most edge of caudal fin to the nearest mm with a measuring board. Weight (W)
was measured to the nearest 0.1 g by an electronic balance (Roy Electronic balance)
after draining the water from the buccal cavity and wiping the moisture content
on the body of fish (King, 1996a).
The lengthweight relationship was calculated separately for each category
based on the methodology of Le Cren (1951). The hypothetical
and parabolic equation used by him is W = aLb. Its logarithmic transformation
is log_{e} W = log_{e} a+b log_{e} L i.e., Y = a+bx
according to Ramaseshaiah and Murthy (1997), where ‘W’
represents weight in g and ‘a’ and ‘b’ the constants, which
were estimated by the method of least squares.
The linear equation was fitted separately for males and females of Mugil
cephalus. Analysis of Covariance (ANCOVA) was employed to test the significance
of difference between regression coefficients (b) at 5% level of both sexes
(Snedecor, 1956; James, 1967; Snedecor
and Cochran, 1967). The ttest (Snedecor and Cochran, 1967)
was employed to test whether the regression coefficient (b) departed significantly
from the expected hypothetical cubic value 3.
RESULTS
The estimated parameters of the lengthweight relationship and other statistical
details of Mugil cephalus are consolidated in Table 1
and 2. The logarithmic values of observed length and corresponding
weights of males and females are plotted in Fig. 1 and 2,
respectively. Similarly the parabolic relationship between length and weight
of males and females of M. cephalus is plotted in Fig.
3 and 4. The regression plots of the data indicated a
linear relationship between the two variables.
Table 1: 
Regression analysis of data for lengthweight relationship
in male and female Mugil cephalus 

b: regression coefficient 
Table 2: 
Analysis of covariance showing difference between regressions
of lengthweight relationship in male and female Mugil cephalus 


Fig. 1: 
Logarithmic relationship between length (TL) and weight (TW)
in male Mugil cephalus 

Fig. 2: 
Logarithmic relationship between length (TL) and weight (TW)
in female Mugil cephalus 
The logarithmic equations derived for males and females of the Mugil cephalus
presently studied are given below:
• 
For males: 
log_{e} W = 1.6349+2.7658 log_{e }L 
• 
For females: 
log_{e} W = 1.7485+2.8586 log_{e }L 
The parabolic relations derived are:
• 
For males: 
W = 0.0232 L^{2.7658} 
• 
For females: 
W = 0.0178 L^{0.9909} 

Fig. 3: 
Parabolic relationship between length and weight of male Mugil
cephalus 

Fig. 4: 
Parabolic relationship between length and weight of female
Mugil cephalus 
Analysis of covariance used to test the difference in regression coefficients
(b) between males and females revealed significant differences (F = 13074.45,
p<0.005). The ttest revealed that the values of regression coefficient (2.7658)
and (2.8586) obtained with 390 males and 450 females, respectively departed
significantly from the cube value (3) at 5% level in the case of males (F =
2.3096; p<.05). However, it was not so in the case of females (F = 1.0158;
p>0.05).
DISCUSSION
From the regression equation obtained in the present study it is clear that
the ‘b’ values traced for males (2.7658) and females (2.8586) were
less than 3, showing the negative allometric pattern of growth. King
(1996a) pointed out that the exponent (b) in the lengthweight relationship
of fishes is usually 3. The ‘b’ value is very close to 3.0 but varies
between 2.5 and 3.5. If the ‘b’ value for fish is 3, the fish grows
isometrically; if it is greater than 3, the fish exhibits positive allometry
and if it is lower than 3 the fish exhibits negative allometry (Tesch,
1968).

Fig. 5: 
Plot of log ‘a’ versus ‘b’ for male and
female Mugil cephalus 
Fishery biologists also stated that the ‘a’ and ‘b’ values
not only differ in different species but differ in the same species depending
on sex, stage of maturity, food habits and so on (Qasim,
1973; Bal and Rao, 1984).
The present study on length weight relationship of M. cephalus showed
that the b value of male (2.7658) differed significantly from the hypothetical
value of 3 (t = 2.8586<0.05), the b value of female (2.8586) did not differ
significantly from the hypothetical value of 3 (t = 1.0158>0.05).values
of both males and females were less than 3. However, differences were found
between the regressions of males and females and hence separate regression equations
were derived for males and females. It can be concluded that the weight in both
sexes of this mullet species increases in proportion 2.7658 for males and 2.8586
for females, if not exactly in proportion of 3. Several factors are responsible
for the minor difference in b values of males and females, such as differential
metabolic rates and growth rates, status of ovarian maturation, reproductive
potential and fullness of stomach or intensity of feeding during analysis, food
and feeding habits, biochemical make up, environmental conditions etc.
In general, the values of the relationship between length and weight obtained
in the present study are very similar to those found by other investigators
who carried out studies in coastal lagoons and marine areas. The results obtained
for M. cephalus in the present study agree well with those of King
(1996b), Garcia et al. (1998) and Haimovici
and Velasco (2000). The ‘a’ and ‘b’ values obtained
for M. cephalus were superimposed in the plot of log ‘a’ versus
‘b’ available for M. cephalus and 1700 miscellaneous species
in Fish Base 2004 for comparison and is shown in Fig. 5. Estimated
values in the present study fall well within the range of values reported earlier
for M. cephalus.
ACKNOWLEDGMENT
Authors are thankful to the Dean and Director, T. Balasubramanian, CAS in Marine
Biology, Faculty of Marine Science, Annamalai University, Parangipettai for
his encouragement and provided facilities.

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