Length – Weight and Length – Length Relationships ...philjournalsci.dost.gov.ph/images/pdf/pjs_pdf/vol146no1/length_weight... · TL were also determined using linear regression

Philippine Journal of Science146 (1): 85-94, March 2017ISSN 0031 - 7683Date Received: ?? Feb 20??

Key words: Arius, comparative growth, gonadosomatic index, fishery management, reproductive period

Length – Weight and Length – Length Relationships, Condition Factor, Sex Ratio and Gonadosomatic Index of

the Ariid Catfishes Arius dispar and Arius manillensis (Siluriformes: Ariidae) in Laguna de Bay, Philippines

1Institute of Biology, College of Science, University of the Philippines, 1101 Diliman, Quezon City, Philippines

2Institute of Human Genetics, National Institutes of Health, University of the Philippines Manila, 625 Pedro Gil St, Ermita, Manila, 1000 Philippines

3Department of Biology, College of Science, Bicol University, 4500 Legazpi City, Philippines

*Corresponding author: [email protected]

Brian S. Santos1, Reynand Jay C. Canoy1, 2, Jazzlyn M. Tango-Imperial1,3, and Jonas P. Quilang1*

The ariid catfishes Arius dispar and Arius manillensis are commercially important in the Philippines and have been overexploited in the past. This study describes for the first time the length-weight and length-length relationships, condition factor, sex ratio, and gonadosomatic index of the two species. A total of 1,698 A. dispar and 874 A. manillensis were collected from Laguna de Bay over the period of 12 months to assess the aforementioned parameters. For both species, the sex ratio significantly differed from equality, the length-length relationships were highly significant and the coefficients of determination (r2) were all greater than 0.96. Length frequency analysis indicates overfishing for both species. The average monthly gonadosomatic index (GSI) ranged from 0.04 to 0.15 in A. dispar males and from 0.23 to 2.99 in females. The average monthly GSI ranged from 0.04 to 0.49 in A. manillensis males and from 0.28 to 4.02 in females. For females of each of the two species, the GSI had two peaks: one from February to May (dry months) and the other from July to September (wet months). These peaks might correspond to the spawning runs of these two species. This study provides baseline information which can be used for the management and conservation of these economically important fishery resources.

INTRODUCTIONThe ariid catfishes Arius dispar Herre, 1926 and A. manillensis Valenciennes, 1840 are both commercially important in the Philippines. A. dispar is a native species in the Philippines and is found also in Taiwan and possibly northern Borneo (Kailola 1999). The species A. dispar

was described and named by Herre in 1926 from the specimens he obtained from Laguna de Bay, Pasig River, and Quiapo Market in Manila. Arius manillensis is an endemic species in the Philippines. Both species, locally known as kanduli, are found in Laguna de Bay, the largest lake in the Philippines, with an area of about 90,000 ha and an average depth of 2.8 m. The lake is located on the Philippine island of Luzon and lies in about 14°0’0” N latitude and 121°5’59” E longitude. In addition to A.

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dispar and A. manillensis, three other species of kanduli have been reported in Laguna de Bay, namely, Arius goniaspis, A. thalassinus, and Hemipimelodus manillensis (Herre 1926; Aldaba 1931). Mane (1929) and Aldaba (1931) reported that commercial catches of kanduli consisted mainly of A. manillensis and that the other species were very rare. Only A. dispar and A. manillensis were found in this study and in the study by Vallejo (1985), Santos and Quilang (2012), and Yu and Quilang (2015). Kanduli used to be the most abundant among all the fishes found in Laguna de Bay (Mane 1929; Aldaba 1931), but beginning the early 1930s, depletion of the fishery resources for kanduli had been noted (Villadolid 1933, 1934). Kanduli have become very rare in the 1960s (Delmendo & Bustillo 1968) and 1970s (Mercene 1978). The populations of kanduli have recovered since then so that in a survey conducted in 1995-1996, among all the fishery resources in the lake, the average annual fish catch for kanduli (reported by the authors as A. manillensis) was the third highest at 516.9 MT (Palma et al. 2002). The yield (catch) to biomass ratio, however, was 4.4, indicating a state of overexploitation (Palma et al. 2002). Despite the economic importance of these fishery resources, very few studies have been conducted on them. Mane (1929) conducted a preliminary study on the feeding, spawning, breeding, and migratory habits of A. manillensis. Stomach content analysis revealed that mature fish is largely carnivorous, consuming mainly fish, snails, shrimps, crabs, earthworms, and insects, and to a lesser extent, vegetable matter (Mane 1929). About 40% of the diet of young fish consisted of algae and plant materials such as duckweed; the remaining portion consisted of animals such as crustaceans, mollusks, earthworms, and fish (Mane 1929). Mane (1929) also observed that kanduli are initially pelagic, but as the breeding season approaches, mature fish gather in schools and migrate to the deeper portions of the lake where they spawn. After spawning, mature spent females leave the breeding ground and the fingerlings that develop then move to the shore. Delmendo (1968) also studied the food and feeding habits of Arius sp. (exact species not indicated) in Laguna de Bay. In addition to food items such as shrimp, snail, fish, chironomid larvae, insects, and vegetable materials, Delmendo (1968) found sand and silt particles in the stomach of kanduli, which indicated that they are bottom feeders. To date, there is no study yet specifically on the biology of A. dispar. All the other studies conducted on kanduli (Arius spp.) were on the possible causes of depletion and suggested regulatory measures for proper management (Villadolid 1933, 1934), fish catch landing statistics and on the types of fishing gears used to catch the species (Aldaba 1931; Delmendo & Bustillo 1968; Mercene 1978, 1987).

This study was aimed at determining the length-weight relationships, length-length relationships, condition factor, sex ratio, and gonadosomatic index of A. dispar and A. manillensis. This study provides baseline information which can be useful to fishery managers and policy makers for the sound management and conservation of the two species. The mathematical description of length and weight can be used to convert one into the other (Tesch 1968). When one is in the field, it is easier, faster, and more accurate to measure length than it is to measure weight. Further, length-weight relationships may be used to infer differences between stocks or populations or differences between the stages in the life history of a species (Le Cren 1951). Length-length relationships for fork length, total length and standard length are also considered very useful for comparative growth studies (Moutopoulos & Stergiou 2002; Hossain et al. 2006; Dadzie et al. 2008). Differences in condition factors can be used as measure of the fatness, well-being, or the suitability of the environment to a species (Le Cren 1951).

MATERIALS AND METHODSA total of 1,698 A. dispar (907 males and 791 females) and 874 A. manillensis (230 males and 644 females) were collected monthly from Laguna de Bay beginning October 2009 until September 2010. The specimens were obtained from local fishermen who caught the fish using gill nets and fish traps. The specimens were transported on ice; measurements and dissection were immediately done upon arrival in the laboratory. The specimens were identified based on species descriptions and identification keys in Conlu (1986), Herre (1926), Kailola (1999), Ferraris (2007), and Marceniuk & Menezes (2007). The most striking difference between A. manillensis and A. dispar is their palatal tooth patch morphology. A. manillensis has palatal tooth patches that are more oval than elongate, while A. dispar has small and widely separated tooth patches (Kailola 1999). Aside from these, the two species are similar morphologically.

Standard length (SL), total length (TL), and fork length (FL) were measured to the nearest 0.1 cm. Body weight (BW) was taken to the nearest 0.1 g and gonad weight (GW) to the nearest 0.0001 g. The sex of each fish was determined by examining the gonads. Standard length (SL; measured in cm) and BW (in g) were log-transformed and the length-weight relationship was determined using the allometric equation BW = a ×SLb, where a and b are regression parameters. Linear regression of Log10BW on Log10SL was done to determine length-weight relationship separately for males and females and both sexes combined for each monthly collection and for the pooled samples.

Quilang et al.: Length-Weight and Gonadosomatic Index of Arius species

Philippine Journal of ScienceVol. 146 No. 1, March 2017

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Following Zar (2010), comparison of regression parameter b between males and females for each species was done using t-test and comparison between months was done using Analysis of Covariance (ANCOVA). Length-length relationships of TL vs SL, SL vs FL, and FL vs TL were also determined using linear regression analysis. The Fulton condition factor (K) was computed for each specimen using the equation: K = (BW∕SL3) × 100. The gonadosomatic index (GSI) was computed using the equation: GSI (%) = GW ×100 ∕ (BW– GW). All statistical analyses were performed using SPSS software (SPSS, Chicago, IL, USA). The length-frequency analysis wizard on FishBase (Froese 2004) was used to determine the extent of overexploitation of the two species.

RESULTSOf the 1,698 Arius dispar specimens, 907 (53.4%) were males and 791(46.6%) were females; the sex ratio was 1.15 male: 1 female, which differed significantly from

equality ( χ 2 = 7.925, P = 0.005). On the other hand, of the 874 A. manillensis specimens, 230 (26.3%) were males and 644 were females (73.7%); the sex ratio of 2.8 females:1 male also differed significantly from equality

( χ 2 = 196.105, P = 1.48×10-44). The length frequency distributions for both species are shown in Figures 1 and 2. For both species, the graphs are approximately bell-shaped. For male specimens of A. dispar, 20%

Figure 1. Length frequency distribution of Arius dispar from Laguna de Bay, Philippines. No. of specimens: males = 907; females = 791.

Figure 2. Length frequency distribution of Arius manillensis from Laguna de Bay, Philippines. No. of specimens: males = 230; females = 644.



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have standard lengths (SL) between 10 and 16 cm, 68% between 17 and 20 cm, and 12% between 21 and 30 cm. For female specimens, 12% have SL between 11 and 16 cm, 68% between 17 and 20 cm, and 20% between 21 and 34 cm. For the male specimens of A. manillensis, 11% have SL between 13 and 16 cm, 71% between 17 and 20 cm, and 18% between 21 and 28 cm. For females, 5% have SL between 13 and 16 cm, 59% between 17 and 20 cm, and 36% between 21 and 36 cm. For A. manillensis, 36 cm constitutes a new maximum length. For both species, specimens below 10 cm were not included in the study because of the difficulty in determining their sexes and identifying their species.

The regression parameters and the coefficients of determination for the length-weight relationships (LWR) are given in Table 1 for A. dispar and Table 2 for A. manillensis. The b values for male specimens of A. dispar varied between 2.7 (October and November) and 3.3 (April). The b values for female specimens varied between 3.0 (November) and 3.5 (April). When all the samples in all the months were pooled, the b values for all the specimens, for all males only, and for females only, were 3.2, 3.1, and 3.3, respectively, all indicating positive allometric growth. The slope for males was significantly different from females (P value < 0.001). ANCOVA also showed significant difference when slopes were compared between months (P < 0.01). On the other hand, the slopes for the male specimens of A. manillensis varied between 2.8 (June) and 3.6 (July). The slopes for female specimens varied between 2.8 (September) and 3.4 (January, July, and August). Pooled samples for all the months gave b values of 3.1 for males only and 3.3 for females only and for both sexes combined, also indicating positive allometric growth. The slope for male specimens of A. manillensis was significantly different from females (P value < 0.01). When males and females were combined and the regression equation was computed for each month, ANCOVA showed significant difference between months (P value < 0.01). The coefficients of determination (r2) for LWR ranged from 0.85 to 0.98 and from 0.91 to 0.98 for A. dispar males and females, respectively. When both sexes were combined for each month, r2 values ranged from 0.90 to 0.98. For A. manillensis, r2 values ranged from 0.87 to 0.995, 0.88 to 0.99, 0.89 to 0.99 for males, females, and for both sexes combined, respectively.

The length-length relationships (LLRs) are given in Table 3 for A. dispar and Table 4 for A. manillensis. The r2 values for both species are greater than 0.96. All LLRs were also highly significant (P value < 0.001). Based on the length-frequency analysis wizard, the length with optimum yield (Lopt) was 23.3 cm for A. manillensis and 22.0 cm for A. dispar. For both species, the frequency peaks at length

classes below the Lopt. The percentage of specimens below Lopt-10% was 62.9% for A. manillensis and 75.7% for A. dispar. The percentage of specimens above Lopt+10% was 2.7% for A. manillensis and 1.9% for A. dispar.

The average monthly Fulton’s condition factor (K) ranged from 1.31 to 1.55 in A. dispar males and from 1.32 to 1.60 in females (Figure 3). The mean K (1.47) of all the 907 A. dispar males was significantly different from the mean K (1.41) of all the 791 females (P value < 0.001). For either of the sexes, there were significant differences in mean K between months (P value < 0.001). For A. manillensis, monthly K ranged from 1.34 to 1.62 for males and from 1.38 to 1.65 in females (Figure 4). The mean K (1.42) for all the 230 A. manillensis males was significantly different from the mean K (1.49) of all the 644 females (P value < 0.001). There were also significant differences in mean K between months for each of the sexes (P value < 0.001).

The average monthly gonadosomatic index (GSI) ranged from 0.04 to 0.15 in A. dispar males and from 0.23 to 2.99 in females. The average monthly GSI ranged from 0.04 to 0.49 in A. manillensis males and from 0.28 to 4.02 in females. For both species the GSI in females starts to rise in February, reaches its peak in April then falls until June and then peaks again in July until September and then falls from October until January (Figures 5 and 6).

DISCUSSIONThe two Arius species are always hauled together when fished. They look very similar externally and can only be distinguished from each other by opening the mouth of the fish and examining the shape of the palatal tooth patch. Since the gears used were nonselective and the effort exerted in catching the two species were the same, A. dispar can be considered the more abundant species as it outnumbers the endemic A. manillensis by 2:1. In contrast, Mane (1929) and Aldaba (1931) reported that the kanduli population in Laguna de Bay and in markets near the lake consisted predominantly of A. manillensis.

The sex ratio for both species differed significantly from the expected 1:1. Quite notably, A. manillensis specimens exhibited a sharp deviation from equality with only a fourth of the sample being males whereas for A. dispar, almost 47% are males. Although large female bias in sex ratio has been observed in other catfish species (Liang et al. 2005), the difference in the sex ratio observed between A. manillensis and A. dispar is remarkable considering the two species are very similar in many other aspects.



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Table 1. Monthly descriptive statistics and regression parameters of length-weight relationships for males, females, and both sexes combined for Arius dispar from Laguna de Bay, Philippines. M, males; F, females; n, number of individuals; a, intercept; b, slope; CI, confidence interval; r2, coefficient of determination.

MonthSex N

Standard length (cm) Regression parameters 95% CI of b r2

min max a b

October 2009 M 16 17.0 22.2 0.0347 2.687 2.288−3.086 0.937

F 17 15.6 25.8 0.0107 3.096 2.766−3.427 0.964

M+F 33 15.6 25.8 0.0174 2.925 2.677−3.174 0.949

November 2009 M 64 13.9 24.4 0.0324 2.708 2.457−2.960 0.882

F 55 13.9 21.6 0.0128 3.045 2.854−3.236 0.951

M+F 119 13.9 24.4 0.0192 2.898 2.734−3.063 0.912

December 2009 M 111 10.8 24.5 0.0132 2.995 2.846−3.144 0.936

F 83 10.9 23.2 0.0090 3.135 2.999−3.270 0.963

M+F 194 10.8 24.5 0.0111 3.057 2.955−3.160 0.948

January 2010 M 64 10.3 29.9 0.0096 3.134 3.026−3.242 0.982

F 33 11.2 26.3 0.0080 3.208 3.054−3.362 0.983

M+F 97 10.3 29.9 0.0087 3.173 3.087−3.259 0.983

February 2010 M 180 11.9 29.6 0.0120 3.046 2.935−3.158 0.942

F 98 13.7 24.7 0.0100 3.117 2.943−3.292 0.929

M+F 278 5.2 29.6 0.0114 3.066 2.972−3.161 0.937

March 2010 M 130 15.2 27.9 0.0080 3.194 3.078−3.309 0.959

F 119 15.1 27.2 0.0057 3.317 3.171−3.463 0.946

M+F 249 15.1 27.9 0.0070 3.244 3.154−3.335 0.953

April 2010 M 28 16.4 23.6 0.0058 3.317 2.966−3.669 0.935

F 40 16.9 23.8 0.0039 3.460 3.142−3.777 0.928

M+F 68 16.4 23.8 0.0043 3.419 3.196−3.641 0.934

May 2010 M 60 17.8 28.9 0.0153 2.964 2.639−3.289 0.852

F 55 17.0 32.3 0.0082 3.182 2.932−3.431 0.925

M+F 115 17.0 32.3 0.0095 3.128 2.937−3.320 0.903

June 2010 M 59 14.4 28.4 0.0150 2.972 2.787−3.157 0.948

F 35 14.7 26.4 0.0067 3.244 3.073−3.416 0.978

M+F 94 14.4 28.4 0.0110 3.079 2.948−3.210 0.960

July 2010 M 47 15.5 23.7 0.0087 3.177 2.948−3.406 0.946

F 62 16.1 34.2 0.0093 3.1668 3.007−3.329 0.963

M+F 109 15.5 34.2 0.0080 3.212 3.092−3.332 0.963

August 2010 M 77 13.8 22.2 0.0115 3.080 2.851−3.309 0.905

F 84 16.6 24.5 0.0075 3.237 3.011−3.462 0.909

M+F 161 13.8 24.5 0.0081 3.207 3.051−3.362 0.913

September 2010 M 71 14.6 25.6 0.0142 3.027 2.775−3.279 0.893

F 110 15.5 23.5 0.0102 3.153 2.969−3.337 0.914

M+F 181 14.6 23.5 0.0108 3.129 2.981−3.276 0.907

Overall M 907 10.3 29.9 0.0099 3.119 3.068−3.170 0.942

F 791 10.9 34.2 0.0066 3.273 3.219−3.327 0.948

M+F 1698 10.3 34.2 0.0078 3.208 3.171−3.245 0.944



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Table 2. Monthly descriptive statistics and regression parameters of length-weight relationships for males, females, and both sexes combined for Arius manillensis from Laguna de Bay, Philippines. M, males; F, females; n, number of individuals; a, intercept; b, slope; CI, confidence interval; r2, coefficient of determination.

Month Sex nStandard

length (cm)Regression parameters 95% CI of b r2

min max a b

October 2009 M 5 17.4 23.5 0.0042 3.413 2.744−4.081 0.989

F 11 17.0 25.2 0.0080 3.197 2.728−3.667 0.963

M+F 16 17.0 25.2 0.0067 3.259 2.935−3.583 0.971

November 2009 M 5 15.8 20.8 0.0038 3.456 1.593−5.319 0.921

F 30 16.0 23.4 0.0081 3.197 2.840−3.553 0.923

M+F 35 15.8 23.4 0.0071 3.241 2.931−3.550 0.932

December 2009 M 7 14.6 20.6 0.0056 3.327 3.055−3.598 0.995

F 27 14.2 25.4 0.0052 3.338 3.179−3.497 0.987

M+F 34 14.2 25.4 0.0056 3.310 3.170−3.450 0.986

January 2010 M 11 14.7 26.2 0.0049 3.363 3.022−3.703 0.982

F 18 13.0 29.0 0.0041 3.434 3.264−3.604 0.991

M+F 29 13.0 29.0 0.0043 3.413 3.266−3.559 0.988

February 2010 M 65 13.4 28.0 0.0164 2.946 2.757−3.135 0.939

F 108 14.9 30.4 0.0066 3.268 3.137−3.398 0.959

M+F 173 13.4 30.4 0.0092 3.149 3.040−3.258 0.950

March 2010 M 43 15.5 25.6 0.0059 3.295 3.046−3.545 0.945

F 146 16.1 33.0 0.0071 3.240 3.085−3.395 0.922

M+F 189 15.5 33.0 0.0066 3.262 3.132−3.392 0.929

April 2010 M 7 17.2 20.6 0.0079 3.202 1.956−4.448 0.897

F 42 17.4 26.0 0.0059 3.316 3.044−3.587 0.938

M+F 49 17.2 26.0 0.0054 3.343 3.098−3.588 0.941

May 2010 M 26 17.7 22.6 0.0100 3.099 2.731−3.466 0.926

F 55 17.2 33.1 0.0103 3.108 2.961−3.254 0.972

M+F 81 17.2 33.1 0.0088 3.153 3.013−3.294 0.962

June 2010 M 21 16.5 21.7 0.0249 2.795 2.268−3.322 0.866

F 41 16.2 36.0 0.0077 3.207 3.044−3.371 0.976

M+F 62 16.2 36.0 0.0076 3.210 3.069−3.351 0.972

July 2010 M 12 15.9 21.0 0.0025 3.588 2.979−4.198 0.945

F 53 17.0 28.2 0.0051 3.377 3.032−3.723 0.883

M+F 65 15.9 28.2 0.0032 3.521 3.249−3.793 0.914

August 2010 M 18 17.6 24.4 0.0136 3.036 2.675−3.397 0.952

F 51 16.2 27.0 0.0047 3.391 3.194−3.588 0.961

M+F 69 16.2 27.0 0.0059 3.314 3.146−3.483 0.958

September 2010 M 10 17.1 20.7 0.0155 3.014 2.115−3.912 0.882

F 62 16.7 24.0 0.0267 2.837 2.564−3.110 0.878

M+F 72 16.7 24.0 0.0238 2.875 2.629−3.121 0.886

Overall M 230 13.0 36.0 0.0107 3.095 2.988−3.203 0.934

F 644 13.4 28.0 0.0066 3.269 3.206−3.331 0.942

M+F 874 13.0 36.0 0.0068 3.256 3.202−3.309 0.943



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Table 3. Length-length relationships between total length (TL), standard length (SL) and fork length (FL) of Arius dispar from Laguna de Bay, Philippines.

Sex Equation n a b r2

Male TL = a + bSL 907 0.945 1.160 0.976

SL = a + bFL -0.229 0.971 0.990

FL = a + bTL -0.029 0.862 0.974

Female TL = a + bSL 791 1.012 1.165 0.961

SL = a + bFL -0.102 0.962 0.990

FL = a + bTL 0.055 0.856 0.965

Combined TL = a + bSL 1,698 0.885 1.167 0.969

SL = a + bFL -0.137 0.965 0.990

FL = a + bTL 0.049 0.857 0.971

Table 4. Length-length relationships between total length (TL), standard length (SL) and fork length (FL) of Arius manillensis from Laguna de Bay, Philippines.

Sex Equation n a b r2

Male TL = a + bSL 230 0.423 1.190 0.980

SL = a + bFL 0.068 0.955 0.991

FL = a + bTL -0.025 0.862 0.987

Female TL = a + bSL 644 0.315 1.199 0.972

SL = a + bFL 0.448 0.937 0.969

FL = a + bTL 0.297 0.848 0.961

Combined TL = a + bSL 874 0.301 1.199 0.975

SL = a + bFL 0.356 0.941 0.974

FL = a + bTL 0.233 0.850 0.967

Figure 3. Monthly averages of Fulton’s condition factor for Arius dispar from Laguna de Bay, Philippines. No. of specimens: males = 907; females = 791. Error bars represent standard error of the means.

Figure 4. Monthly averages of Fulton’s condition factor for Arius manillensis from Laguna de Bay, Philippines. No. of specimens: males = 230; females = 644. Error bars represent standard error of the means



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The b values computed in this study fall between 2 and 4 and are close to 3; the values that are usually obtained for fishes (Tesch 1968). These values usually differ between species, between stocks or populations within species, between different stages of development, between sexes, or depending on differences in environmental conditions (Le Cren 1951; Tesch 1968; Froese 2006). The r2 values for LWR are relatively high, which shows that the length measurements are good determinants of weight.

There is only one published study on LWR of A. dispar, but the regression equation was based only on three individuals collected from Candaba wetland in the Philippines (Garcia 2010). Hence, this is the first

Figure 6. Monthly averages of gonadosomatic index for Arius manillensis from Laguna de Bay, Philippines. No. of specimens: males = 230; females = 644. Error bars represent standard error of the means.

Figure 5. Monthly averages of gonadosomatic index for Arius dispar from Laguna de Bay, Philippines. No. of specimens: males = 907; females = 791. Error bars represent standard error of the means.

comprehensive study on the LWR of this commercially important fish species in the Philippines. To date and to our knowledge, there is no published or unpublished study yet on the LWR of A. manillensis.

Only 17.7% of A. manillensis and 15.2% of A. dispar consist of mature specimens. This estimate may have been affected by sampling error, since some female specimens with SL lower than Lm were observed to have ripe gonads. Nonetheless, the presence of immature specimens is evident from the sample. Likewise, majority of the specimens collected were below the margin of optimal yield. These are indicators of overfishing (Froese 2004).



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Condition factor was observed to vary significantly between species, between sexes, and between different months. Differences in condition factor could be attributed to variability in fatness, suitability of the environment or stage in the development of the gonad (Le Cren 1951). GSI for both species was much higher from April to September 2010 compared to the other months, although there was a marked depression in the month of June. Mature ovaries and large ova were observed during the peak months, which could be the spawning runs for both species. The first period corresponds to the summer months, while the second one corresponds to the onset of the rainy season. The occurrence of two spawning periods is not surprising as these Ariidae species are batch spawning fishes (Mane 1929). Results of the present study also confirm the account of Aldaba (1931) that based on the observations of fishermen, spawning of kanduli takes place during the height of the dry season, from February to May, with the greatest spawning activity occurring in March and April. For A. manillensis, Mane (1929) reported that spawning lasts from middle of February to the first week of May and that during the breeding season, spawning runs take place during the middle of February, middle of March, middle of April, and first week of May. Mane (1929) inferred these four spawning runs by measuring the diameter of 300 ova from 10 fish examined each month from September 1927 to June 1928. No measurements were made by Mane (1929) for the months of July and August. In this study, for both A. manillensis and A. dispar, in addition to the dry months (February to May), July and August are also peak months for spawning. In other Siluriform species, the reproductive period draws its cues from the amount of rainfall (Liang et al. 2005; Hossain et al. 2006). Although these involve only one spawning period throughout the year, there are other fish species that exhibit biannual spawning period (Hussain and Abdullah 1977; Gill et al. 1996).

In summary, this study provides basic information on the length-weight relationships, length-length- relationships, condition factor, sex ratio, and gonadosomatic index of A. dispar and A. manillensis. These two species are commercially important and overfished in the Philippines, thus the information provided by this study may be used for the proper fishery management and conservation of these biologically important resources. Froese (2004) proposed three indicators of overfishing that can be used by fishery managers and applied for Arius spp. given the data and observations in this study. The first is to ensure that all fish catches are reproductively mature. Mane (1929) estimated that A. manillensis in Laguna de Bay matures at 14.4-16.5 cm. In the current study, however, standard lengths of 10.3 cm and 13.0 cm for A. manillensis and A. dispar, respectively, were reported while fish as small as 7.0 cm were observed in catches. Second, only those within 10% of the optimal length should be caught. For both

species, more than half were smaller than Lopt-10%. Last, individuals above Lopt+10% are deemed mega-spawners and should also be excluded from the catches. Although low in frequency, large specimens were also present in the samples. These results show that these species are still overexploited. Aside from regulating the sizes of fish included in catches, it is also important to consider the month of the year and ensure maximal spawning occurs. Results from this study show that spawning peaks from February to May (dry season) and from July to September (wet season). If seasonal closure during the peak months is not possible, the mega-spawners and extremely gravid females could be excluded from the catch. These regulatory measures have to be enforced by local governments and concerned government agencies to prevent these valuable fishery resources from being depleted again.

ACKNOWLEDGMENTSThis study was funded through a PhD Incentive Grant (Project No: 090921) awarded to J.P. Quilang by the Office of the Chancellor of the University of the Philippines Diliman through the Office of the Vice-Chancellor for Research and Development. Special thanks also to the Institute of Biology, University of the Philippines Diliman for logistical support.

REFERENCESALDABA VC. 1931. The kanduli fishery of Laguna de

Bay. Philipp J Sci 45:29-39.

CONLU PV. 1986. Guide to Philippine flora and fauna. Vol IX. Manila, Philippines: National Resources Management Center, Ministry of Natural Resources, and University of the Philippines. 495p.

DADZIE S, ABOU-SEEDO F, MANYALA JO. 2008. Length-length relationship, length–weight relationship, gonadosomatic index, condition factor, size at maturity and fecundity of Parastromateus niger (Carangidae) in Kuwaiti waters. J Appl Ichthyol 24 (3):334-336.

DELMENDO MN. 1968. Food and feeding habits of the economic species of fish in Laguna de Bay. Proceedings of the Indo-Pacific Fisheries Council, 13th Session, Brisbane, Queensland, Australia. Bangkok, Thailand: IPFC Secretariat, FAO Regional Office for Asia and the Far East. p. 143-161.

DELMENDO MN, BUSTILLO RN. 1968. Studies on fish population of Laguna de Bay. Proceedings of the Indo-Pacific Fisheries Council, 13th Session, Brisbane, Queensland, Australia. Bangkok, Thailand: IPFC



93

Secretariat, FAO Regional Office for Asia and the Far East. p. 1-23.

GARCIA LMB. 2010. Species composition and length-weight relationship of fishes in the Candaba wetland on Luzon Island, Philippines. J Appl Ichthyol 26(6):946-948.

FERRARIS CJ. 2007. Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types. Zootaxa 1418:1-628.

FROESE R. 2004. Keep it simple: Three indicators to deal with overfishing. Fish Fish 5(1):86-91.

FROESE R. 2006. Cube law, condition factor and weight–length relationships: History, meta-analysis and recommendations. J Appl Ichthyol 22(4):241-253.

GILL HS, WISE BS, POTTER IC, CHAPLIN JA. 1996. Biannual spawning periods and resultant divergent patterns of growth in the estuarine goby Pseudogobius olorum: temperature-induced? Marine Biol 125(3): 453-466.

HERRE AW. 1926. A summary of the Philippine catfishes, order Nematognathi. Philipp J Sci 31:385-413.

HOSSAIN MY, AHMED ZF, LEUNDA PM, JASMINE S, OSCOZ J, MIRANDA R, OHTOMI J. 2006. Condition, length–weight and length–length relationships of the Asian striped catfish Mystus vittatus (Bloch, 1794) (Siluriformes: Bagridae) in the Mathabhanga River, southwestern Bangladesh. J Appl Ichthyol 22(4): 304-307.

HUSSAIN NA, ABDULLAH MAS. 1977. The length-weight relationship, spawning season and food habits of six commercial fishes in Kuwaiti waters. Indian J Fish 24 (1 & 2):181-194.

KAILOLA PJ. 1999. Ariidae. In: Carpenter KE, Niem VH, ed. FAO species identification guides for fishery purposes: The living marine resources of the Western Central Pacific. Rome: FAO. p. 1827-1879.

LE CREN ED. 1951. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca fluviatilis). J Animal Ecol 20(2): 201-219.

LIANG SH, WU HP, SHIEH BS. 2005. Size structure, reproductive phenology, and sex ratio of an exotic armored catfish (Liposarcus multiradiatus) in the Kaoping River of southern Taiwan. Zool Stud 44(2): 252-259.

MANE AM. 1929. A preliminary study of the life history and habits of kanduli (Arius spp.) in Laguna de Bay. Philipp Agric Sci 18:81-118.

MARCENIUK AP, MENEZES NA. 2007. Systematics of the Family Ariidae (Ostariophysi: Siluriformes), with a Redefinition of the Genera. Zootaxa 1416:1-126.

MERCENE EC. 1978. Kanduli population survey of Laguna de Bay. Philipp J Fish 16(1):1-24.

MERCENE EC. 1987. A survey of Laguna de Bay open water fishery. Fish Res J Philipp 12(1-2):17-28.

MOUTOPOULOS DK, STERGIOU KI. 2002. Length-weight and length-length relationships of fish species from Aegean Sea (Greece). J Appl Ichthyol 18(3): 00-203.

PALMA AL, DIAMANTE AS, POL RM. 2002. An assessment of fishery resources of Laguna de Bay. Aquat Ecosyst Health 5(2):139-146.

SANTOS BS, QUILANG JP. 2012. Geometric morphometric analysis of Arius manillensis and Arius dispar (Siluriformes: Ariidae) populations in Laguna de Bay, Philippines. Philipp J Sci 141(1):1-11.

TESCH FW. 1968. Age and growth. In Ricker WE ed. Methods for assessment of fish production in fresh waters. Oxford and Edinburg: Blackwell Scientific Publications. p. 93-123

VALLEJO AN. 1985. Fisheries of Laguna de Bay. Nat App Sci Bull 37(4):285-346.

VILLADOLID DV. 1933. Some causes of depletion of certain fishery resources of Laguna de Bay. Nat Appl Sci Bull 3:251-256.

VILLADOLID DV. 1934. Kanduli fisheries of Laguna de Bay Philippine Islands: Remedial and regulatory measures for their rehabilitation. Philipp J Sci 54: 545-552.

Yu SCS, QUILANG JP. 2015. Morphological and molecular analysis of the sea catfishes Arius manillensis and Arius dispar (Siluriformes: Ariidae). Philipp Agric Sci 98(1):32–46.

ZAR JH. 2010. Biostatistical analysis. 5th ed. Upper Saddle River, New Jersey, USA: Prentice Hall. 960p.



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Length – Weight and Length – Length Relationships ...philjournalsci.dost.gov.ph/images/pdf/pjs_pdf/vol146no1/length_weight... · TL were also determined using linear regression