Estimating length-weight parameters for food fish is an important component in the population dynamics studies. The present study was carried out to find the length-weight relationship parameters of tropical Scomberoides lysan (Forsskal 1775) from the northern waters of Sri Lanka. Weekly samples were collected from the commercial catches during January 2010 to December 2010. A total of 892 specimens (299 males, 354 females and 239 unsexed) were analyzed. Curvilinear relationships of length-weight relationships for male, female and unsexed obtained were W = 0.0037*L3.1319, W = 0.0058*L3.0048 and W = 0.0179*L2.6496, respectively. Comparison of regression co-efficient of male, female and unsexed using GLMANCOVA revealed that the b values show significant differences (p<0.05) between each other. The exponent values 3.1319 for male and 2.6496 for unsexed were significantly different (p<0.05) from 3, whereas, the value 3.0048 for female did not deviate significantly (p>0.05) from 3. From the statistical analysis it can be concluded that males exhibit positive allometric growth, females exhibit isometric growth and unsexed exhibit negative allometric growth. The parameters obtained from the study are useful fundamental factors applicable in future culture trials as well as in population dynamics studies.
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Understanding the length-weight relationship parameters plays a major role in fisheries biology and population dynamics (Sivashanthini, 2008). Studies on length-weight relationship provide information about their growth level (Okgerman, 2005). Measuring the weight of live fish in the field is very difficult and time consuming (Morato et al., 2001). Various authors revealed that information on length-weight relationship is required to determine the conversion of growth-in-length equations to growth-in-weight. These conversions can be used in stock assessment models. It can also be used in the estimation of biomass from length observations and estimation of the condition of the fish and this relationship is useful for comparison of life histories of certain species between regions (De La Cruz Aguero et al., 2011; Goncalves et al., 1996; Moutopoulos and Stergiou, 2002).
Using the length-weight relationships, the well-being of individuals can be assessed. Okgerman (2005) derived the condition factor form the length-weight relationship for Scardinius erythrophthalmus from the Sapanca Lake. The b values of 3.3731 and mean condition of 1.243 were recorded in his study. The differences between separate unit stocks of the same species can also be determined by these parameters (King, 2007). Moreover, estimating length-weight parameters is essential to compare the growth pattern in fisheries management (Moutopoulos and Stergiou, 2002).
Previous studies show that several researchers reported the length-weight parameters not only for finfish but also for fish related organisms from various parts of the world. Few examples for such research work on finfish are studies made by Ayoade (2011) for African carp Labeo ogunensis, Lawson et al. (2011) for frill fin goby, Bathygobius soporator, Elp et al. (2006) for Barbel, Barbus plebejus ercisianus, Hosseini et al. (2009) for Sphyraena jello and by Sivashanthini et al. (2009a) for Sphyraena obtusata. One related study available for fish related organism is the study made by Sivashanthini et al. (2009b) for squid, Sepioteuthis lessoniana. It is evident from the literature survey that the length-weight relationship of Scomberoides lysan have not been studied, so far and this is the first study for S. lysan.
The genus Scomberoides is classified under family Carangidae; and four species of Scomberoides have been recorded from the Sri Lankan waters, such as S. lysan, S. commersonianus, S. tol and S. tala (De Bruin et al., 1995). No information is available on the biology or length-weight relationship of the above four species from the Sri Lankan waters. S. lysan is commonly known as double spotted queen fish found in the tropical areas of Indian and Pacific Ocean. These are one of the economically important large food fish found in coastal as well as offshore fisheries in Sri Lanka (De Bruin et al., 1995). It is more popular for dry fish production and has high export value. Therefore, the present study has been carried out to find the length-weight relationship parameters of tropical Scomberoides lysan using morphometric measurements from the northern waters of Sri Lanka.
MATERIALS AND METHODS
Sample collection: Northern part of Sri Lanka is situated between 79°E to 80°E longitude and 9°N to 10°N latitudes in the Indian ocean. Samples were collected weekly from the commercial catches at Passaiyoor, Delft, Karainagar and Point Pedro landing centers during January 2010 to December 2010, using a specific drift gill net for Genus Scomberoides with the mesh size of 7", 21 ply (Katta valai). Beach seines and trap net (Kalankatti valai) fixed in shallow waters are also operated to caught S. lysan in waters around Jaffna peninsula.
Morphometric measurements: Total Length (TL) of each fish was measured from the anterior most edge of the lower lip (tip of snout) to the distal part of the caudal fin to the nearest mm with a measuring board and Total Weight (TW) was measured to the nearest 0.1 g by an electronic balance (AND, HF-1200G). All specimens were sorted by sex according to the morphological analysis of gonads as male, female or unsexed.
Regression analysis: The relationship between the length and weight of a fish is usually expressed by the equation W = a L b (Ricker, 1973); where, W is the weight of the fish, L is the total length, a is the intercept and b is the slope. If a fish is growing isometrically (increasing in all dimensions at the same rate) and doubles in length, its weight will increase in relation to the increase in volume; that is by 8 (or 23) times (King, 2007). Thus there is a cubic relationship between length (L) and weight (W) and b is close to 3 in isometric growths and a is a constant determined empirically.
Statistical analysis: Weights and lengths of male, female and unsexed were log transformed and the resulting linear relationship fitted by the computer based linear regression analysis. Significance of the regression was assessed by General Linear Model Analysis of Covariance (GLMANCOVA). The b values obtained for male, female and unsexed were tested by Students t-test to see whether the b values differ significantly from 3 or not (Zar, 1999). Two sample t-test was performed to compare the mean weight data of male and females to distinguish the significant difference between male and female. All statistical analysis was done by MINITAB (Version 14) statistical software and the significance level was tested at 95% confidence interval.
RESULTS AND DISCUSSION
A total number of 892 fish (299 males, 354 females and 239 unsexed) were analyzed. Length range of fish collected is 22.2-62.5 cm for males, 22.0-71.0 cm for females and 14.6-36.1 cm for unsexed. The estimates of the regression parameters for male, female and unsexed are given in Table 1. The r2 values obtained while calculating the regression parameters are 0.9485 for males, 0.9490 for females and 0.9435 for unsexed. For male, female and unsexed S. lysan obtained residual degrees of freedom are 297, 352 and 237 whereas residual sum of squares are 1.505861, 1.348065 and 0.590727, respectively. Linear regression relationships between total length and weight of male, female and unsexed S. lysan are given in Table 2. Curvilinear relationships obtained for male, female and unsexed are W = 0.0037 L 3.1319, W = 0.0058 L 3.0048 and W = 0.0179 L 2.6496, respectively.
The results of students t-test to analyze the significance of variation in the estimates of b for S. lysan from the expected value for the ideal fish (3.0) are as follows:
|•||Male||(3.1319-3)/0.0424 = 3.1159 Significant (Computed ta (2),0.05, 298 > 1.97)|
|•||Female||(3.0048-3.0)/0.0371 = 0.1305 Not significant (Computed ta (2)0.05, 353 < 1.97)|
|•||Unsexed||(2.6496-3.0)/0.0421 = 8.3144 Significant (Computed ta (2)0.05, 238 > 1.97)|
Student t-test showed that the b values obtained for male and unsexed were significantly different (p<0.05) from 3 indicating positive allometric growth for male and negative allometric growth for unsexed whereas the b value obtained for female very close to 3, did not deviate significantly (p>0.05) from 3 indicating isometric growth.
|Table 1:||Length-weight relationship parameters of S. lysan|
|N: No. of observations, df: Degrees of freedom, b: Regression exponent, a: Constant, SS: Sum of squares, r: Correlation coefficient|
|Table 2:||Linear regression relationship between total length and weight of male, female and unsexed S. lysan|
|Table 3:||Parameters obtained from two-sample t-test for mean weight of males and female of S. lysan|
|Fig. 1:||Percentage frequency of total length distribution of male, female and unsexed S. lysan|
Correlation coefficient (r2) 0.9485 for males, 0.9490 for females and 0.9435 for unsexed found to be significant (p<0.001) in all instances indicating good correlation between length and weight of S. lysan.
Comparison of regression co-efficient of male, female and unsexed using GLMANCOVA for the regression of log weight on log total length for S. lysan male, female and unsexed revealed the b values show significant differences (p<0.05) between each other. The confidence intervals of a value for male, female and unsexed do not overlap with each other and therefore there is a significant difference between the intercepts, too.
Results of the two sample t-test are given in Table 3. It showed that males were significantly (p>0.05) heavier than females. The frequency distribution of total length for male, female and unsexed S. lysan individuals is shown in Fig. 1. Highest percentage of frequency (50.4%) was observed for S. lysan individuals of 21-30 cm total length class interval.
Length-weight relationship of fish and fish related organisms have been studied widely in all parts of the world by several authors. Different values for the exponent coefficient (b) for different fish have been recorded in different parts of the world. Earlier, Allen (1938) pointed out that the exponent coefficient (b) computed from the length-weight relationship of fishes is usually 3. Later, Carlander (1969) pointed out that the b value is very close to 3.0 but varies between 2.5 and 3.5. This statement could be supported by the previous work carried out for various fish species for example 3.171 for Amblygaster sirm, 3.24 for Carcharhinus albimarginatus (Kulbicki et al., 1993); 2.459 for Sepioteuthis lessoniana (Sivashanthini et al., 2009b); 3.359 for Leuciscus cephalus Karatas and Faith CAN (2005); 2.880 for Tenualosa ilisha (Ahmed et al., 2008) and 2.929 for Atherina sp. (Bouriga et al., 2011). These b values cannot be simply compared for consistency as these are different species with different metabolic rate.
Widely accepted concept is that if the exponent value is 3, the fish grows isometrically, if it is greater or less than 3 fish grows allometrically (Tesch, 1968). The b value depends on several factors such as age, body shape and amount of fat present, sex, maturity stage, season, temperature, salinity and available nutrient food (Moutopoulos and Stergiou, 2002). Taskavak and Bilecenoglu (2001) and Ozaydin and Taskavak (2006) stated that the parameter b in the length-weight relationship vary seasonally, even daily and between habitats.
Length-weight relationship of S. lysan have not been studied in Sri Lanka, so far and this is the first study to compute such parameters. Some of the earlier results on length-weight relationship of Scomberoides species from other parts of the world are shown in Table 4. In New Caledonia and South Africa b value of 2.896 and 2.685 was obtained, respectively for S. lysan (Letourneur et al., 1998). But b value of 2.937 was obtained for S. tol from Karnataka waters, India (Abdurahiman et al., 2004). The b value obtained in the present study for male (3.1319) and female (3.0048) is slightly higher than the previously recorded values. It may be due to the variations in ecology of the geographical locations, food availability and different environmental conditions. However the a and b values obtained for male and female S. lysan were superimposed in the plot of log a versus b available for S. lysan, Carangidae and 1300 miscellaneous species in FishBase 2011 (Froese and Pauly, 2011) and it is shown in Fig. 2a and b. The parameters obtained from the study are useful fundamental factors applicable in future culture trials as well as in population dynamics studies.
|Table 4:||The parameters of length-weight relationships of genus Scomberoides from different regions of the world ( SL = standard length, FL = Fork length, TL = Total length)|
|Fig. 2a:||Plot of log a versus b for male S. lysan (Black dot indicates the current estimate; X axis denotes exponent coefficient b and Y axis denotes constant log a). Source: FishBase 2011|
|Fig. 2b:||Plot of log a versus b for female S. lysan (Black dot indicates the current estimate; X axis denotes exponent coefficient b and Y axis denotes constant log a). Source: FishBase 2011|
Length-weight relationships for male, female and unsexed S. lysan were W = 0.0037*L3.1319, W = 0.0058*L3.0048 and W = 0.0179*L2.6496, respectively. Comparison of regression co-efficient of male, female and unsexed using GLMANCOVA revealed that the b values show significant differences (p<0.05) between each other. The statistical analysis confirmed that males exhibit positive allometric growth, females exhibit isometric growth and unsexed exhibit negative allometric growth. The parameters obtained can be applied in future culture trials and in population dynamics studies.
Authors are grateful to the authorities of National Research Council, Colombo, Sri Lanka for the financial assistance in the form of research grant (Grant No. 07-19).
- Abdurahiman, K.P., T. Harishnayak, P.U. Zacharia and K.S. Mohamed, 2004. Length-weight relationship of commercially important marine fi shes and shellfi shes of the Southern Coast of Karnataka, India. NAGA WorldFish Center Quart., 27: 9-14.
- Kulbicki, M., G.M. Tham, P. Thollot and L. Wantiez, 1993. Length-weight relationships of fish from the lagoon of New Caledonia. Naga ICLARM Quart., 16: 26-30.
- Letourneur, Y., M. Kulbicki and P. Labrosse, 1998. Length-weight relationships of fish from coral reefs and lagoons of New Caledonia, Southwestern Pacific Ocean: An update. Naga ICLARM Q., 21: 39-46.
- Moutopoulos, D.K. and K.I. Stergiou, 2002. Length-weight and length-length relationships of fish species from the Aegean Sea (Greece). J. Applied Ichthyol., 18: 200-203.
- Ozaydin, O. and E. Taskavak, 2006. Length-weight relationhips for 47 fish species from Izmir Bay (Eastern Agean Sea, Turkey). Acta Adriat., 47: 211-216.
- Sivashanthini, K., 2008. Length-weight relationships and condition of gerreids (Pisces: Gerreidae) from the Parangipettai waters (SE coast of India). Asian Fish. Sci., 21: 405-419.
- Zar, J.H., 1999. Biostatistical Analysis. 4th Edn., Prentice-Hall, New Jersy, USA., Pages: 469.
- Goncalves, J.M.S., L. Bentes, P.G. Lino, J. Ribeiro, A.V.M. Canario and K. Erzini, 1997. Weight-length relationships for selected fish species of the small-scale demersal fisheries of the South and South-West Coast of Portugal. Fish. Res., 30: 253-256.