Age and growth of cutlassfishes, Trichiurus spp., from the South China Sea.

Abstract--Age and growth of two species of cutlassfishes, Trichiurus spp. (Trichiuridae), from the South China Sea were examined. Between December 1996 and November 1997, 1495 specimens were collected from coastal waters near Hong Kong. Two species, Trichiurus lepturus and T. nanhaiensis, were harvested and ages of specimens were estimated by using transverse sections of the sagittal otoliths. Opaque growth rings were verified to have formed annually during February. Lee's phenomenon was not observed for either species, although T. lepturus tended to display reverse Lee's phenomenon. Otolith weight was linearly related to age, and accounted for about 72% and 76% of the variation in age (t) for T. lepturus and T. nanhaiensis, respectively, comparable to the von Bertalanffy growth models in preanal length (PL). For older fish, otolith weight provided a more precise estimate of age than preanal length. Preanal length and age were fitted to the von Bertalanffy growth model by nonlinear regression, resulting in

PL (mm) = 589{1 - [e.sup.[-0.168 (t + 2.682)]]}

(T. lepturus);

PL (mm) = 602{1 - [e.sup.[-0.207 (t + 2.044)]]}

(T. nanhaiensis).

Growth in length of the two species was significantly different (ANCOVA, [F.sub.2,1245]=169.69, P [is less than] 0.001).

The cutlassfish, Trichiurus lepturus Linnaeus 1758, occurs throughout tropical and temperate waters of the world, between latitude 60 [degrees] and 45 [degrees] S (Froese and Pauly, 1997). World harvests are approximately 750,000 tonnes annually and China lands about 80% (600,000 tonnes) (Claus, 1995). In terms of weight, cutlassfish is the most important commercial marine fish species in China (Luo, 1991) and has accounted for about 10% to 20% of the total marine fish catch. It is caught in all Chinese seas, the Bo Hai, the Yellow Sea, the East China Sea, and the South China Sea (Jiang et al., 1991), and about 15% of the catch comes from the South China Sea (Fig. 1) (Liu, 1996). Cutlassfish is used as food fish and is caught mainly by bottom trawling (Luo, 1991) and in lower amounts by longline, hand line, gill net, drift net and purse seine (Chen and Liu, 1982).

[Figure 1 ILLUSTRATION OMITTED]

Age and growth studies and their derived growth parameters are indispensable in determining stock dynamics (Brouard et al., 1984). Numerous age and growth studies of T. lepturus have been conducted over the past few decades (Table 1); however, most research has focused on northern populations in the East China Sea, the Yellow Sea, and the Bo Hai. Similar work on populations in the South China Sea has not been available.

[TABULAR DATA 1 NOT REPRODUCIBLE IN ASCII]

Three species of trichiurids occur in the South China Sea, T. lepturus, T. nanhaiensis (Wang and Xu, 1992, in Wang et al., 1992), and T. brevis (Wang and You, 1992, in Wang et al., 1992), whereas only one species, T. lepturus, occurs in the waters of China farther north (Wang et al., 1992, 1993, 1994). Populations of T. lepturus in the Bo Hai, the Yellow Sea, and the East China Sea suffer from overfishing (Lin, 1985; Du et al., 1988; Ma and Xu, 1989; Luo, 1991; Ye and Rosenberg, 1991; Xu et al., 1994). It is harvested only in the Bo Hai and the Yellow Sea as bycatch in other fisheries (Lin, 1985). The condition of trichiurid stocks in the South China Sea remains unclear.

Numerous methods have been used to age trichiurids. The length-frequency method has proven useful in India (Narasimham, 1976; Chakraborty, 1990) and the Philippines (Ingles and Pauly, 1984). Yet, hard parts such as whole or sectioned otoliths and vertebral centra are most frequently used to age cutlassfish (Table 1). Measuring otolith weight or otolith size may be a cost-effective method for aging some fishes (Barbieri et al., 1994; Ferreira and Russ, 1994; Worthington et al., 1995). Although sectioned otoliths are reliable for aging fish, the method is time consuming and expensive (Beckman et al., 1991).

The aims of our study were 1) to validate age estimates by using transverse sections of sagittal otoliths; 2) to verify Lee's phenomenon; 3) to evaluate the potential of using otolith size and weight to estimate age; 4) to fit the age-length data to the von Bertalanffy growth model; and 5) to provide age-growth information for management of cutlassfish resources from the South China Sea.

Materials and methods

Between December 1996 and November 1997, 960 specimens (preanal length [PL] range:138-468 mm; PL=the tip of the lower jaw with the mouth closed to the middle of anus) of T. lepturus, and 535 specimens (PL range:253-551 mm) of T. nanhaiensis were obtained from commercial catches in the coastal waters of Hong Kong. Commercial gears included longlines, purse seines and bottom trawls. Fresh specimens were placed on ice, transported to the laboratory, and identified by using the diagnostic key of Wang et al. (1992, 1993): if the frontal bone split laterally, specimens were identified as T. lepturus, otherwise T. nanhaiensis. Preanal lengths were measured to the nearest mm. Specimens were blotted dry and weighed (whole and gutted) to the nearest 0.01 g. To estimate the relationship between PL and gutted weight (W), the variables were log-transformed to meet the assumptions of normality and homogeneous variance. A linear version of the power function: W (g) = a [PL.sup.b] (mm) was fitted to the data.

Distinct growth rings on whole otoliths and vertebral centra were ill-defined. Transverse sections of sagittal otolith yielded "readable" growth rings; the latter were chosen as aging tools. Left and right sagittae were weighed independently to the nearest 0.01 mg after being oven dried at 40 [degrees] C for 30 min. Otolith length (OL) was measured to the nearest 0.05 mm with calipers. Sagittal otoliths were embedded in resin and sectioned transversely through the nucleus with a low-speed saw. Up to five sections, 0.3 to 0.5 mm thick, were made from each otolith to ensure that at least one passed through the center of the nucleus. Sections were then ground with 1000- and 1200-grit sand paper, mounted on glass slides with clear fingernail polish, and examined with a compound microscope at 40x magnification with transmitted light. The relative age in years was determined by counting the number of opaque growth rings on the dorsal side of the sectioned otoliths (Fig. 2). Thirty-five pairs of sectioned otoliths of both species were processed. No differences in the number of growth rings were found in left and right sections of each pair. Thereafter, the right sagitta was used for age determination.

[Figure 2 ILLUSTRATION OMITTED]

Otoliths were read twice (one month apart) in a random order, with no knowledge of fish length or species. Precision was measured by the percentage of agreement between readings (Lowerre-Barbieri et al., 1994). Deviations were counted a third time. Only counts with at least two agreements were used in subsequent analyses. Marginal increment method was used to validate the reading of annuli. Otolith radius (OR), otolith annular radius (OAR), and marginal increment (MI) (Fig. 2) were measured with an ocular micrometer to the nearest 0.025 mm.

The tendency for older fish to reflect smaller back-calculated length at earlier ages than measured length is known as Lee's phenomenon (Smith, 1983), and is related to size-selective mortality (Boehlert et al., 1989). To evaluate this phenomenon, the mean otolith annular radius (MOAR) for each annulus of the same age group was calculated, and the MOAR for each annulus of different age groups was plotted against the age group (Yamaguchi et al., 1990). Thus, we determined if older fish demonstrated slower growth of hard parts at younger ages, i.e. true Lee's phenomenon (Smale and Taylor, 1987). The ANOVA test was used to compare MOARs among different age groups.

Multiple linear-regression models were fitted in a stepwise manner to predict age from otolith weight and length. Variables were log-transformed to meet the assumptions of normality and homogeneous variance. A paired-sample t-test showed no significant difference between left and right sagittal otoliths in terms of weight (T. lepturus: t=-0.097, df=917, P [is greater than] 0.90; T. nanhaiensis: t=-0.762, df=518, P [is greater than] 0.44) and length (T. lepturus: t=-0.471, df=916, P [is greater than] 0.45; T. nanhaiensis: t=-0.689, df=523, P [is greater than] 0.49). Therefore, average otolith length and weight were used in the analyses. For all the linear regressions mentioned above, analysis of covariance (ANCOVA) was used to compare regressions between sexes and species.

We assigned 1 May and 1 June as the birth dates for T. lepturus and T. nanhaiensis, respectively (Kwok and Ni, 1999). Relative ages derived from aging were then converted to absolute ages. Von Bertalanffy growth curves were fitted by nonlinear regression on age and preanal length data (SPSS vers. 7.5). The von Bertalanffy growth equation for length is

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

where [PL.sub.[infinity]] = the asymptotic length;

k = growth coefficient; and

[t.sub.0] = the hypothetical age at zero length.

Plots of residuals from regression models were used to check the assumption of normality. ANCOVA was used to compare log-transformed age-at-length regressions between sexes and species.

Results

The preanal length (mm) and gutted weight (g) regression models were significantly different between sexes (ANCOVA: T. lepturus: [F.sub.2,932]=4.00, P [is less than] 0.05; T. nanhaiensis: [F.sub.2,530]=3.34, P [is less than] 0.05) and species (ANCOVA: [F.sub.2,1466]=83.76, P [is less than] 0.001). The regression models were

T. lepturus

males:

W = 1.513 x [10.sup.-4] [PL.sup.2.571] (n=212, [r.sup.2]=0.9777, P [is less than] 0.001);

females:

W = 1.748 x [10.sup.-4] [PL.sup.2.549] (n=724, [r.sup.2]=0.9761, P [is less than] 0.001);

sexes combined:

W = 1.624 x [10.sup.-4] [PL.sup.2.561] (n=936, [r.sup.2]=0.9771, P [is less than] 0.001);

T. nanhaiensis

males:

W = 3.363 x [10.sup.-5] [PL.sup.2.846] (n=282, [r.sup.2]=0.8506, P [is less than] 0.001);

females:

W = 6.553 x [10.sup.-5] [PL.sup.2.729] (n=252, [r.sup.2]=0.9299, P [is less than] 0.001);

sexes combined:

W = 5.672 x [10.sup.-5] [PL.sup.2.755] (n=534, [r.sup.2]=0.8968, P [is less than] 0.001).

Sectioned sagittae of both species had an opaque nucleus located above the sulcal groove toward the dorsum. The nucleus was surrounded by a pattern of alternating wide, translucent zones and thin, opaque zones; the latter were considered annuli (Fig. 3). Annuli were distinct on the dorsum of the sections but were usually indecipherable on the ventral side. A total of 757 and 534 otoliths were embedded in resin and sectioned for T. lepturus and T. nanhaiensis, respectively. Of these, 33 (4.3%) and 9 (1.7%) were unreadable, and the percentage agreement between the two readings for each species was 95.4% and 92.7%, respectively.

[Figure 3 ILLUSTRATION OMITTED]

The least marginal increment values (Fig. 4) occurred in February for both species, suggesting that one growth ring (annulus) formed each year. Only specimens age 1-4 were included in the analyses because older fish were rare in our collections. The mean otolith annular radius (MOAR) of the first annulus (ANOVA: [F.sub.5,582]=3.046, P [is less than] 0.05) and third annulus (ANOVA: [F.sub.3,80]=4.024, P [is less than] 0.05) of T. lepturus were significantly different among different age groups (Fig. 5); MOARs increased slightly with older age groups. However, no particular trend was found with regard to the MOARs of T. nanhaiensis (Fig. 5). Lee's phenomenon was not evident for either species, although reverse Lee's phenomenon was possible for T. lepturus.

[Figures 4-5 ILLUSTRATION OMITTED]

Otolith weight accounted for 68.7% and 68.9% (Table 2) of the variability in age for T. lepturus and T. nanhaiensis, respectively. A negligible amount of the remaining variability was explained by considering otolith length in addition to otolith weight. The otolith weight-age regression was improved by fitting the untreated variables (otolith weight and age) with simple linear regression models:

[TABULAR DATA 2 NOT REPRODUCIBLE IN ASCII]

T. lepturus:

OW = 6.3533 + 5.2913Age (n=718, [r.sup.2]=0.7168, P [is less than] 0.001);

T. nanhaiensis:

OW = 6.3921 + 3.6850Age (n=515, [r.sup.2]=0.7561, P [is less than] 0.001).

These regression results suggest a linear relationship between otolith weight and age (Fig. 6). The regression models were significantly different between the two species (ANCOVA: [F.sub.2,1229]=224.17, P [is less than] 0.001). Normal probability and residual plots showed that the regressions complied with the assumptions of normality and homogeneous variance.

[Figure 6 ILLUSTRATION OMITTED]

Von Bertalanffy growth equations for both species were

T. lepturus

males:

PL = 755.2 {1 - [e.sup.[-0.116 (t + 2.737)]]} (n=146, [r.sup.2]=0.684, P [is less than] 0.001);

females:

PL = 601.4 {1 - [e.sup.[-0.158 (t + 2.850)]]} (n=578, [r.sup.2]=0.765, P is less than] 0.001);

sexes combined:

PL = 589.1 {1 - [e.sup.[0.168 (t + 2.682)]]} (n=724, [r.sup.2]=0.749, P is less than] 0.001);

T. nanhaiensis

males:

PL = 501.7 {1 - [e.sup.[-0.306 (t + 1.673)]]} (n=281, [r.sup.2]=0.682, P [is less than] 0.001);

females:

PL = 612.6 {1 - [e.sup.[-0.220 (t + 1.792)]]} (n=244, [r.sup.2]=0.726, P is less than] 0.001);

sexes combined:

PL = 602.1 {1 - [e.sup.[-0.207 (t + 2.044)]]} (n=525, [r.sup.2]=0.699, P [is less than] 0.001).

Von Bertalanffy growth curves for sexes combined are depicted in Figure 7. No systematic trend was found in the residual plots for all regressions. The [t.sub.max] (age at 95% of asymptotic length) of T. lepturus and T. nanhaiensis were 15.1 and 12.4 years, respectively. The [W.sub.[infinity]] (asymptotic weight: estimated by substituting [PL.sub.[inifinity]] to the preanal length-weight equations) of T. lepturus and T. nanhaiensis were 2025 g and 2585 g, respectively. Log-transformed age-at-length regressions were significantly different between sexes (ANCOVA: T. lepturus: [F.sub.2,720]=4.39, P [is less than] 0.05; T. nanhaiensis: [F.sub.2,521]=23.78, P [is less than] 0.001) and species (ANCOVA: [F.sub.2,1245]=169.69, P [is less than] 0.001).

[Figure 7 ILLUSTRATION OMITTED]

Discussion

Our aging study of cutlass fishes from the South China Sea was successful in that we 1) found distinct growth rings on sectional sagittal otolith, 2) had excellent precision in independent ring counts, and 3) used marginal increment analyses to validate our aging method. In general, cutlassfishes from the northern seas of China (Misu, 1958, 1964; Hamada, 1971; Sakamoto, 1976; Hong, 1980; Wu et al., 1985a; Du et al., 1988; Hanabuchi, 1989; El-Haweet and Ozawa, 1996) and the South China Sea (our study) deposit annuli in late winter or early spring, suggesting that ring formation likely occurs in response to reduced water temperatures and is not correlated with peak spawning as indicated in Chen and Lee (1982). Summer is the peak spawning period of T. lepturus and T. nanhaiensis in the South China Sea (Kwok and Ni, 1999).

El-Haweet and Ozawa (1996) questioned whether Lee's phenomenon existed in a trichiurid population from Japan, having found no indication of Lee's or reverse Lee's phenomenon. We found that T. lepturus may exhibit reverse Lee's phenomenon, which suggests that T. lepturus are not overfished in the South China Sea or that fishing mortality is not size-selective, or that both situations may apply. Alternatively, fast growing individuals in the T. lepturus population may have greater chances of survival and attain older ages.

The linear relation between otolith weight and age (Fig. 6) indicates that cutlassfish otoliths continuously increase in weight with age. The regression models explain 72% and 76% of the variance for T. lepturus and T. nanhaiensis, respectively, comparable to the von Bertalanffy growth model in preanal length. Thus, otolith weight provides a more precise estimate of age in older fish. Use of otolith weight to estimate age should be done with caution because these relationships have been shown to be population specific (Worthington et al., 1995).

This study is the first application of nonlinear regression in deriving avon Bertalanffy growth model for the cutlassfish; previously Ford-Walford plots were the most common method. The shortcomings associated with that method include 1) weighing problems due to different sample sizes of each age group; 2) a failure in providing variance-covariance for comparisons; 3) none of the raw data are used (Liu and Yeh, 1991); and 4) a reliance on back-calculated body length, which is usually estimated from the linear regression between hardpart dimension (e.g. otolith radius) and body length. Unfortunately, the growth of otoliths has been shown to be independent of somatic growth (Beckman et al., 1991; Barbieri et al., 1994), i.e. growth of body length ceases with age, while growth of hard parts continue. In comparison, our application of nonlinear regression analysis can avoid all these problems.

Basic growth parameters for these two populations of trichiurids in the South China Sea showed lower growth coefficients and higher asymptotic length, i.e. specimens reached maximum size at a slower pace than other trichiurids from the western Pacific Ocean (Table 1). This finding may be real or may reflect different methods employed for estimating growth.

In our comparison of the two species, T. nanhaiensis possessed a higher growth coefficient (k) than T. lepturus. Male T. lepturus had a lower growth coefficient but attained larger asymptotic size ([PL.sub.[infinity]]) than did female T. lepturus, whereas the opposite held true for T. nanhaiensis.

We provide basic growth parameters for use in the study of stock dynamics of trichiurids in the South China Sea. A formal stock assessment should be conducted with special emphasis on establishing an ecologically sustainable cutlassfish fishery in the South China Sea to prevent overfishing, or even fishery collapse, as has occurred in the northern populations of trichiurids.

Acknowledgments

Helpful assistance by Agassi Cheung and Y. K. Tam is much appreciated. We thank V. A. Unkefer for assistance with the writing and three anonymous reviewers for useful comments. Finally, we thank the Biology Department, Hong Kong University of Science and Technology, for providing the necessary funding and facilities.

Literature cited

Barbieri, L. R., M. E. Chittenden Jr., and C. M. Jones. 1994. Age, growth, and mortality of Atlantic croaker, Micropogonias undulatus, in the Chesapeake Bay region, with a discussion of apparent geographic changes in population dynamics. Fish. Bull. 92:1-12.

Beckman, D. W., A. L. Stanley, J. H. Render, and C. A. Wilson. 1991. Age and growth-rate estimation of sheepshead Archosargus probatocephalus in Louisiana waters using otoliths. Fish. Bull. 89:1-8.

Boehlert, G. W., M. M. Yoklavich, and D. B. Chelton. 1989. Time series of growth in the genus Sebastes from the Northeast Pacific Ocean. Fish. Bull. 87:791-806.

Brouard, E., R., Grandperrin, M. Kulbicki, and J. Rivaton. 1984. Note on observation of daily rings on otoliths of deepwater snapper. ICLARM Translation 3, Manila, Philippines, 8 p.

Chakraborty, S. K. 1990. Fishery, age, growth and mortality estimates of Trichiurus lepturus Linnaeus from Bombay waters. Indian J. Fish. 37:1-7.

Chen, W., and S. Lee. 1982. Age and growth of the ribbonfishes Trichiurus (Perciformes: Trichiuridae) of Taiwan. Bull. Inst. Zool., Academia Sinica 21:9-20.

Chen, Z. C., and J. Q. Liu. 1982. Commercial fishes of South China Sea. Guangdong Science and Technology Press, Guangzhou, China., 266 p. [In Chinese.]

Claus, F. 1995. Multilingual illustrated guide to the world's commercial warmwater fish. Fishing News Book, Cambridge, MA, 215 p.

Du, J. R., F. Z. Li, S. D. Lin, and Q. D. Zhang. 1988. On age and growth of hairtail, Trichiurus haumela (Forskal) in western Taiwan Strait. J. Oceanogr. Taiwan Strait 7:339-346. [In Chinese.]

El-Haweet, A. E., and T. Ozawa. 1996. Age, growth of ribbon fish Trichiurus japonicus in Kagoshima Bay, Japan. Fish. Sci. 62:529-533.

Ferreira, B. P., and G. R. Russ. 1994. Age validation and estimation of growth rate of the coral trout, Plectropomus leopardus, (Lacepede 1802) from Lizard Island, Northern Great Barrier Reef. Fish. Bull. 92:46-57.

Froese, R., and D. Pauly (eds.). 1997. Fishbase--a biological database on fish (software): ICLARM, Manila, Philippines, 256 p.

Hamada, R. 1971. Age and growth of the ribbon fish, Trichiurus lepturus based on the transverse section of the otolith. Bull. Seikai Reg. Fish. Res. Lab. 41:53-62. [In Japanese.]

Hanabuchi, S. 1989. Age and growth of cutlassfish, Trichiurus lepturus in Tsushima waters. Bull. Seikai Reg. Fish. Lab. 67:37-57. [In Japanese.]

Hong, S. 1980. A study on the age and growth of the hairtail in the Po Hai and Huang Hai. J. Fish. China 4:361-370. [In Chinese.]

Ingles, J., and D. Pauly. 1984. An atlas of the growth, mortality and recruitment of Philippine fishes. Institute of Fisheries Development and Research, College of Fisheries, University of the Philippines in the Visayas, Quezon City, Philippines and International Center for Living Aquatic Resources Management, Manila, Philippines. ICLARM Tech. Rep. 13:114-116.

Jiang, S. F., X. Z. Wang, Y. D. Chen, and X. Q. Zeng (eds.). 1991. Compilation of the statistics of Chinese fishery forty years (1949-1988). Department of Fishery, Ministry of Agriculture, The People's of Republic China. China Ocean Press, Beijin, 256 p. [In Chinese.]

Kosaka, M., M. Ogura, H. Shirai and M. Maeji. 1967. Ecological study on the ribbon fish, Trichiurus lepturus LINNE, in Suruga Bay. J. College of Mar. Sci. Tech., Tokai Univ. 2:131-146. [In Japanese.]

Kwok, K. Y. 1999. Reproduction of cutlassfishes, Trichiurus spp. from South China Sea. Mar. Ecol. Prog. Ser. 176:39-47.

Lin, J. Q. 1985. Hairtails. Agriculture Press, Beijing, 88 p. [In Chinese.]

Lin, J. Q., and M. D. Zhang. 1981. On the characteristic of the growth of the hairtail, Trichiurus haumela (Forskal) from the Yellow Sea and Bo-Hai. Mar. Fish. Res. 2:41-56. [In Chinese.]

Liu, C. C., and S. Y. Yeh. 1991. Age determination and growth of red emperor snapper (Lutjanus sebae) in the Arafura Sea off North Australia. ACTA Oceanog. Taiwanica 26:36-52.

Liu, S. L. (ed.) 1996. Compilation of the statistics of Chinese fishery (1989-1993). Department of Fishery, Ministry of Agriculture, the People's of Republic China. China Ocean Press, Beijing, 130 p. [In Chinese.]

Lowerre-Barbieri, S. K., M. E. Chittenden Jr, and C. M. Jones. 1994. A comparison of a validated otolith method to age weakfish, Cynoscion regalis, with the traditional scale method. Fish. Bull. 92:555-568.

Luo, B. 1991. Cutlassfish. In Marine fishery biology (C. Q. Fan, ed.), p. 111-160. Agriculture Press, Beijing. [In Chinese.]

Ma, Y., and J. Xu. 1989. Catch change pattern of hairtail in the East China Sea. Mar. Sci. 5:37-39. [in Chinese with English abstract.]

Misu, H. 1958. Studies on the fisheries biology of the ribbon fish Trichiurus lepturus in the East China and Yellow Seas. 1. On the age and the growth. Bull. Seikai Reg. Fish. Res. Lab. 15:1-14. [In Japanese.]

1964. Fisheries biology on the ribbon fish (Trichiurus lepturus Linne) in the East China and Yellow Seas. Bull. Seikai Reg. Fish. Lab. 32:1-58. [In Japanese.]

Narasimham, K. A. 1976. Age and growth of ribbonfish Trichiurus lepturus Linnaeus. Indian J. Fish. 23:174-182.

Sakamoto, T. 1976. Age and growth of the ribbon fish in the Kii Channel. Bull. Jap. Soc. Sci. Fish. 42:1-11. [In Japanese.]

Smale, M. A., and W. W. Taylor. 1987. Sources of back-calculation error in estimating growth of lake whitefish. In The age and growth of fish (R. C. Summerfelt, and G. E. Hall, eds.), p. 189-202. Iowa State Univ. Press, Ames, IA.

Smith, C. L. 1983. Summary of round table discussions on back calculation. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 8:45-47.

SPSS Inc. 1997. SPSS base 7.5 for Windows. SPSS Inc., Chicago, IL, 628 p.

Suzuki, K., and S. Kimura. 1980. Fishery biology of the ribbon Fish, Trichiurus lepturus, in Kumano-Nada, central Japan. Faculty Fish. Mie Univ. 7:173-192. [In Japanese.]

Wang, K., L. Liu, F. You, and C. Xu. 1992. Studies on the genetic variation and systematics of the hairtail fishes from South China Sea. Mar. Sci. 2:69-71. [In Chinese.]

Wang, K., P. Zhang, L. Liu, F. You, and C. Xu. 1993. Studies on Trichiuridae from China coastal water. ACTA Oceanol. Sin. 15(2):77-83. lin Chinese.]

Wang, K., P. Zhang, L. Liu, F. You, C. Xu, and J. Wang. 1994. Biochemical assessment of the taxonomic status of Trichiuridae population from China Coastal water. ACTA Oceanol. Sin. 16(1):93-104. [In Chinese.]

Worthington, D. G., P. J. Doherty, and A. J. Fowler. 1995. Variation in the relationship between otolith weight and age: implications for estimation of age of two tropical damselfish (Pomacentrus moluccensis and P. wardi). Can. J. Fish. Aquat. Sci. 52:232-242.

Wu, H., G. Cheng, and J. Wang. 1985a. A study of the ageing of hairtails, Trichiurus haumela (Forskal). Oceanol. Et Limnol. Sinica 16:408-416. [In Chinese.]

Wu, H., G. Cheng, J. Zhou, and J. Wang. 1985b. Study of the growth of the hairtails, Trichiurus haumela (Forskal). Oceanol. Et Limnol. Sinica 16:156-167. [In Chinese.]

Xu, H., Z. Liu, Y. Ding, and Y. Xu. 1994. Resource condition and management countermeasure of largehead hairtail in East China Sea. J. Zhejiang Coll. Fish. 13:5-11. [In Chinese.]

Yamaguchi, Y., N. Hirayama, A. Koike, and H. A. Adam. 1990. Age determination and growth of Oreochromis niloticus and Sarotherodon galilaeus in High Dam Lake, Egypt. Nippon Suisan Gakkaishi (Bull. Jap. Soc. Fish.) 56:437-443.

Ye, Y., and A. A. Rosenberg. 1991. A study of the dynamics and management of the hairtail fishery, Trichiurus haumela, in the East China Sea. Aquat. Liv. Res. 4:65-75.

Kai Yin Kwok I-Hsun Ni Department of Biology Hong Kong University of Science & Technology Hong Kong SAR, China E-mail address (for I-H Ni, contact author): [e-mail]