Length-weight relationship, fish species, growth type, Southern Black Sea.
Length-weight data are widely used to gather information
on biology of fishes. In general, this and other different kind
of analysis have become one of the standard methods used in
fisheries biology (Le Cren, 1951; Kohler et al., 1995). These data
are necessary in estimation of the growth rates, age and length
composition of fish populations (Kohler et al., 1995). In fish,
size is generally more biologically relevant than age, mainly
because several ecological and physiological factors are more
size-dependent than age. Consequently, variability in size has
important implications in diverse aspects of fisheries science and
population dynamics (Erzini, 1994). A length- weight relationship
(LWR) presents useful information for understanding the relative
condition of fish stocks. In addition, LWR is used in various
important applications for evaluation of fish stocks (Ricker, 1968;
Pauly, 1993; Garcia et al., 1998; Haimovici and Velasco, 2000).
Some of these applications include assessment of available fish stock and comparison of fish populations existing in different
regions (Petrakis and Stergiou, 1995). Furthermore, length-weight
(L-W) relationships have special importance in fisheries research
because they (a) are used to convert growth-in-length equations
to growth-in-weight in stock assessment models, (b) allow the
estimation of the biomass of a species from length frequency
distributions, (c) the condition of fish; and (d) are useful for
between region comparisons of life histories of a certain species
(Gonçalves et al., 1997; Binohlan and Pauly, 2000).
The aim of this study is to determine the length-weight
relationships of 10 fish species, most of which are demersal
species caught by gill and trammel nets in the Eastern Black Sea
of Turkey. The reported results may contribute to management of
fisheries resources in the area.
Materials and Methods
Samples were collected from the monthly fishing trials
performed between June 2010 and June 2011 in the Eastern Black Sea coasts of Turkey. Fish specimens were collected using gill and
trammel nets at depths ranging from 8 m to 95 m. The length of
gill and trammel nets consisting of five different mesh sizes (16,
17, 18, 20, 22 mm bar length) were 639 m and 590 m, respectively.
The total length (TL) and weight (W) of each fish were measured
to the nearest 0.1 cm and 0.01 g, respectively. The relationships
between length and weight is expressed by W = a × Lb, which
was converted to linear form as lnW = lna + b lnL, where W is
total body weight (g), L is the total length (cm), a = intercept
and b = slope regression coefficients (Ricker, 1973; King, 2007).
When b values equal to 3, less than and higher than 3, then fish
species in questions is said to show isometric, negative allometric
and positive allometric growth, respectively. (Bagenal and Tesch,
1978; Santos et al., 2002). The b value for each species was tested
with a t-test at the 0.05 level of significance to verify whether it
was significantly different from the predicted values for isometric
growth (Morey et al., 2003). For this test, the following equation
was used (Sokal and Rohlf, 1987);
ts = (b - 3) / sb,
Where ts is the value of t test, b is the slope and sb is the
standard error of b. Analysis of covariance (ANCOVA) was used
to determine whether there was significant difference in slopes
between sexes (Zar, 1999).
Results and Discussion
A total of 5353 individuals belonging to 10 fish species
sampled during in the study. The sample size ranged from 11
individuals for Parablennius gattorugine to 2705 for Merlangius
merlangus euxinus. Table 1 presents the sample sizes, the minimum
and maximum L-W values, the coefficients of determination (r2),
regression coefficients and the growth types of each species. In
order to compare the results of the present study with those of
other length-weight relationship studies in different areas were
presented in Table 2. The length-weight relationship parameter,
b value, generally ranges between 2 and 4 (Bagenal and Tesch,
1978), often close to 3 (Jobling, 2002). The b values ranged from
2.549 for E. encrasicolus to 3.301 for S. porcus with mean value
of 3.070 ± 0.039 (S.E.). The coefficient of determination (r2) value was calculated 0.901 for S. solea and 0.974 for E. encrasicolus
with mean value of 0.935 ± 0,007 (S.E.). Five, four and one species
showed isometric, positive allometric and negative allometric
growth, respectively. Analysis of covariance (ANCOVA) showed
that the differences in slopes(b values) between the sexes for E.
encrasicolus, M. merlangus, M. barbatus, S. porcus, S. solea, S.
maena and U. scaber were significant (P < 0.05).
Table 1. Descriptive statistics and estimated parameters of length-weight relationship of 10 fish species caught by gillnet and trammel
nets in the Eastern Black Sea, Turkey.
Table 2: Some study results of length-weight relationship for the fish species in different areas.
The length-weight relationship varies among species according
to genetically body shape and to the condition of individuals of
a fish species. The condition sometimes reflects the presence of
nutrients and the growth before in the sampling week, but condition
is variable and dynamic. Individuals within the same sampling
considerably vary, however, the average condition of individuals
in each population differs according to years and seasons. For
some species, sex and gonad development are important variables
(Schneider et al., 2000). Also, many factors such as habitat, diet,
locality, and stomach fullness are the other important variables
that affect the length–weight relationship in fishes (Esmaeili and
This study was supported by the Scientific Research
Fund of Recep Tayyip Erdoğan University (RTEUSRF) with
project number 2010. 103.03.1. We are grateful to Yusuf Ceylan
and boat owner for all of their cooperation and help during the
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