Contributions to the reproductive biology of encrasicholina punctifer Fowler, 1938 (engraulidae) from West Sumatra, Indonesia

Transcription

1 Fisheries Research 44 (1999) 113±120 Contributions to the reproductive biology of encrasicholina punctifer Fowler, 1938 (engraulidae) from West Sumatra, Indonesia Gerd Maack a,*, Michael R. George b a ZMT Center for Tropical Marine Ecology, Bremen, Germany b German Oceanographic Museum, Museum for Marine Research and Fishery Aquarium, Katherinenberg 14/20, Stralsund 18439, Germany Received 6 January 1999; received in revised form 29 June 1999; accepted 17 July 1999 Abstract Encrasicholina punctifer (Fowler, 1938) is economically by far the most important sh species in the coastal area of Padang (West Sumatra, Indonesia). In this study, the reproductive biology of E. punctifer is described for the rst time with different methods. The relationship between length and weight of E. punctifer in the coastal waters of west Sumatra can be described as W ˆ 6:310 6 L 3:125 t r 2 ˆ 0:96; n ˆ The Encrasicholines are multiple spawners with asynchronous oocyte development. During one individual spawning season, oocyte development is a continuous process involving all stages of oocytes, clearly represented by an unimodal oocyte-size-frequency-distribution (OSFD). Before spawning a new batch can be identi ed by its separation from the remaining oocytes, leaving a gap in the OSFD. There are postovulatory follicles inside the ovary after ovulation. From a gonosomatic index of 5.5 the ovaries contain hydrated oocytes, indicating a pre-spawning state. A certain proportion of the population is spawning at any time. The relative fecundity was estimated to be 985 ( 359) eggs per batch and gram female body weight. The oocyte development occurs simultaneously in all areas of the ovary. First maturity is reached at 57.5 mm L t. There is no dependence between sh condition and gonad weight. The necessary energy for the gonadal growth of the anchovies is not obtained from body fat, but most likely directly from forage. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Anchovy; Encrasicholina punctifer; Reproductive biology; Fecundity; Oocyte development 1. Introduction * Corresponding author. Present address: UFZ-Centre for Environmental Research, Department for Chemical Ecotoxicology, Permoserstraûe 15, Leipzig, Germany. Tel.: ; fax: address: gm@.uoe.ufz.de (G. Maack) In many regions of Indonesia, sh is important for the human protein supply and at least 200 species are of commercial interest (Soesanto, 1985). Encrasicholina punctifer (Fowler, 1938) is by far the most economically important species in the coastal area of West Sumatra (Rohdenburg, 1995). It is a small /99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S (99)

2 114 G. Maack, M.R. George / Fisheries Research 44 (1999) 113±120 pelagic schooling sh, with a total length of 10 cm (Paula e Silva, 1992) and a short life span of around a year (Rohdenburg, 1995). The species is commonly found in the coastal waters around the Indian Ocean and in the West Paci c. From Delsman (1931) it is known, that Encrasicholines spawn virtually continuously. He described the species as a multiple spawning sh with asynchronous oocyte development, i.e. oocytes in all stages of development occurring simultaneously in reproductively active ovaries. According to Hunter et al. (1992) multiple spawning sh are called indeterminate serial or batch spawners, if the annual fecundity is not xed at the beginning of spawning and the standing stock of present oocytes in the ovary is continuously replaced by new developing oocytes during one spawning cycle. On the other hand, sh that have a xed fecundity prior to the onset of spawning, are called determinate serial spawners. Engraulis mordax is an example of an indeterminate serial spawner (Hunter and Goldberg, 1980; Hunter and Leong, 1981). In a determinate serial spawner, as for instance the Dover sole (Microstomus paci cus), the standing stock of advanced oocytes-prior to the onset of spawning-is equivalent to the annual fecundity, whereas in an indeterminate serial spawner this is not the case (Hunter et al., 1992). In the latter case annual fecundity is much higher than the present standing stock of advanced oocytes. Determining the type of spawning is of great importance for estimating the potential annual fecundity of a species and its ability to recover from human shery impact. In the coastal area of West Sumatra, there is no management for the artisanal shery and the impact on the standing stock is rising, because more and more people try to earn their living with artisanal shery. In this study the reproductive biology of E. punctifer is described to place basic information on this species at shery management agencies' disposal. Different methods were used for a cross-check of the results. 2. Material and methods E. punctifer was collected twice a week from artisanal shermen, operating the traditional Bagan shery at the coast of Padang (Fig. 1). By this method, sh are attracted by arti cial light and caught with lift nets during the night. Samples for this study were taken from different boats and pooled each week from April to July For length±weight relationship, total length L t (to 1 mm) and body weight (g) of 2550 individuals were measured. For fecundity studies, 780 individuals ranging from 43 to 95 mm L t were sampled. In the laboratory, wet weight, length and gonad weight of the sh were measured. Subsamples were preserved in 4% buffered formalin for histological investigations Gonosomatic index The gonosomatic index (GSI) was determined as follows: GSIˆgonad weight gonad-free body weight 1 100: 2.2. Condition factor The condition factor (CF) was determined as follows by using the total length L t of the sh: CF ˆ gonad-free wet weight L 3:125 t 100: Instead of the theoretical coef cient of b ˆ 3, the actual coef cient of the length±weight regression was used Size at sexual maturity Size at sexual maturity was determined with the GSI-method after Grimes (1976). This method was used to determine the 50% maturity length by calculating the mean GSI per 5 mm length-class. 100xGSI n 100 ˆ proportional increase in GSI: GSI n 1 The resulting values showed the proportional increase or decrease of mean GSI in comparison to the previous length-class. The highest proportional increase of GSI of all classes corresponded to the mean length, where 50% of this species reached maturity Analysis of ovaries For counting and measuring the oocytes, the ovary tissue was preserved in Gilson's uid (Bagenal, 1978)

3 G. Maack, M.R. George / Fisheries Research 44 (1999) 113± Fig. 1. Location where E. punctifer was collected off the coast of Padang-City (hatched field). for three months. Oocytes from the xed tissue were then separated from the ovigerous folds (ovarian lamellae) and measured to the nearest 0.01 mm on their longest axis under a binocular microscope on a digitizer. Ripe ovaries were identi ed from their external appearance and the extent to which they lled the body cavity. The most advanced group of oocytes was counted and the relative batch fecundity (oocytes per g body weight) of each female was estimated. Standard method of Methyleneblue (Gerrits, 1985) was used to stain the ovaries. The ovaries of 30 specimens were examined histologically and classi- ed using Wright's method for E. heteroloba (Wright, 1992). 3. Results The length±weight relationship of E. punctifer off the coast of West Sumatra is Weight ˆ 6:310 6 L 3:125 t ; r 2 ˆ 0:96; n ˆ 2550: No correlation was found between the GSI and the condition factor (r 2 ˆ ) for immature females and for mature females. The progression of maturing oocytes was evident when the upper mode of the oocyte size frequency in the ovaries was plotted against the gonosomatic index (Fig. 2). The maximum mode of the oocyte is constant except when the GSI is between 5 and 9. All oocytes of the spawning batch are fully grown. Furthermore, the scatter of the points suggests, that there is a rapid increase in the oocyte size at maturity. In this study E. punctifer reached sexual maturity at a total length of 55±59 mm. The same length was estimated using histological measures. At a total length of 60 mm postovulatory follicles (POFs) were found in the ovaries. Vitellogenesis appeared in females larger than 57 mm L t. The relation of size at sexual maturity to maximal length was

4 116 G. Maack, M.R. George / Fisheries Research 44 (1999) 113±120 Fig. 2. Relationship between the diameter of the most advanced mode of oocytes in the ovary and gonosomatic index (GSI) of E. punctifer Fecundity Relative batch fecundity of E. punctifer was 985 (359) eggs per g body weight. To nd potential differences between the two ovaries of single females, both ovaries of 13 specimens were counted separately and results compared. There was no signi cant difference in the distribution (p < 0.1) between the left and right ovary of single females. Oocytes of the four different maturity classes were distributed evenly over the entire ovary. Using the t-test, there was no signi cant (p < 0.05) difference in the distribution regarding the proportion of the maturity stages in each of the four divisions of the ovary (Fig. 3). All developmental stages of oocytes occurred in the entire ovary at the same time. The oocytes did not move to the cranial end of the ovary during maturation Oocyte-size-frequency-distribution and histological analysis To examine the primary maturation stages, one representative female was selected to show the typical oocyte-size-frequency-distribution (OSFD) (50 mm size classes) and the histological cross section (Fig. 4a±c). The enormous increase of size and volume of the advanced oocytes is obvious. In a reproductively Fig. 3. Frequency of oocytes in different maturity-classes in the entire ovary in comparison to the frequency in a single quarter of the ovary (1st quarter: caudal end; 4th quarter: cranial end).

5 G. Maack, M.R. George / Fisheries Research 44 (1999) 113± Fig. 4. Combined representation of OSFD, GSI and histological cross section of different maturity stages in the ovary of E. punctifer: (a) immature ovary with unyolked oocytes; (b) maturing ovary with vitellogenic oocytes; (c) ripe ovary with hydrated oocytes shortly before spawning, the batch is clearly visible. U ˆ unyolked oocytes; V ˆ vitellogenic oocytes; H ˆ hydrated oocytes. active ovary, there is no gap in the OSFD. This means the oocyte development is continuous (Fig. 4a and b). The maturation of the oocyte and the growing GSI are also re ected in the increasing average oocyte diameter of the different gonads. The average oocyte diameter is 0.25, 0.3 and 0.5 mm, respectively. Shortly before spawning, the most advanced group of oocytes forms a new batch of hydrated oocytes, clearly separated in the OSFD from the developing oocytes cohort with sizes up to 0.5 mm (Fig. 4c). The diameter of

6 118 G. Maack, M.R. George / Fisheries Research 44 (1999) 113±120 hydrated oocytes range from 0.8 to 1.2 mm x ˆ 0:95 mm ; whereas the average oocyte diameter of the rst cohort is 0.31 mm. In the cross section of an immature ovary, only small unyolked oocytes can be detected (Fig. 4a) usually within a size range of 0.05±0.25 mm. In a maturing ovary, oocytes in different vitellogenic stages are present, (Fig. 4b) while a hydrated ovary contains oocytes in all different developmental stages (Fig. 4c). The three histological photos (Fig. 4a±c): reveal the sequence of oogenesis of E. punctifer: (a) from small cells with basophilic cytoplasm; (b) the intermediate stage of maturing oocytes in different phases of vitellogenesis; and (c) the largest size with dissolving nucleus and fusion of yolk globules during hydration. As shown for other pelagic sh species (George, 1998), vitellogenesis in E. punctifer also starts at the cytoplasm periphery of the oocyte. The oocytes do not move to the cranial end of the ovary during maturation (Fig. 3). The oocytes develop simultaneously in all parts of the ovary. In the histological cross sections postovulatory follicles were detected, indicating that the referring specimen had recently spawned. Postovulatory follicles-if presentalways occur together with vitellogenic oocytes. The follicles consist of two cell layers: the internal granulosa and the very thin external thecal layer. Only a few single atretic (degenerating) oocytes occurred during this study. 4. Discussion The absence of a correlation of the mean CF and the GSI of E. punctifer, as also shown for other pelagic sh species (George, 1996, 1998), con rmed the suggestion of Wright (1989): the condition of the anchovies is not dependent on gonadal weight. The necessary energy for gonad growth is not obtained from body fat, but most likely directly from food. The basic energy requirement is needed for swimming, body function, etc. and only a surplus of energy can be used for oocyte development. Hunter and Leong (1981) estimate 13% of the body weight for Engraulis mordax is necessary for a single batch. That means a change in prey density would have a direct in uence on the fecundity of E. punctifer. The high variability of the batch fecundity found for E. punctifer (Table 1) is similar to that of E. heteroloba (Dalzell, 1987) and E. purpurea (Clarke, 1987). Clarke (1987) explained seasonal differences in terms of water temperature, the temperature in summer in the study area being 58C higher than in winter. Wright (1989) suggested the availability of food as the main reason for regional and temporal differences of the batch fecundity in the genus Encrasicholina. Tiews et al. (1970) observed a spawning peak of E. punctifer, E. heteroloba and E. devisi in Manila Bay during the south-west monsoon, while primary production was very high. Parrish et al. (1986) found an age-speci c fecundity in E. mordax. Variation of mean batch fecundity for a standardised female weight is described for Sardinops sagax, where batch fecundity increased with ovary-free body weight and length of a female (George, 1998). A comparative study of sardines, anchovies and sprats (Alheit, 1989) revealed a higher variability of batch fecundity within a spawning season, than interannual variations of batch fecundity. Additionally, Adrianov et al. (1996) found a marked daily cycle of oocyte development in the Black Sea Anchovy (Engraulis encrasicholus ponticus). The relationship of size at sexual maturity to maximal length with ts very well to L max /L 1 ratio Beverton (1963) found for other Engraulidae. He showed, that the size at sexual maturity is proportional to maximal length. Smaller species reach size at sexual maturity, in proportion to their maximal length, Table 1 Relative batch fecundity and length at sexual maturity (L t mm) of E. punctifer from the Indo-Pacific Country Mean relative batch fecundity S.D. Range N Sexual maturity (L t mm) Author West Sumatra ± ±59 Present study Papua-New- Guinea ± ± 1 Dalzell (1987) India ± ± 1236±8971 ± 45±49 Luther (1989) Philippines ± ± ± ± 65 Tiews et al. (1970)

7 G. Maack, M.R. George / Fisheries Research 44 (1999) 113± faster than larger species (Blaxter and Hunter, 1982). One explanation for the different sizes at sexual maturity found by other authors (Table 1) is that they determined the sexual maturity macroscopically. In a multiple spawning sh with asynchronous oocyte development, without histological analysis it is critical to distinguish developing ovaries from those which nished the individual spawning season and mature ovaries from those which are already partially spent. Important physiological processes like starting of the vitellogenesis and the beginning of the hydration are not macroscopically visible. In a serial spawner the identi cation of postovulatory follicles is the only way to nd a partially spawned ovary. All this is only possible after histological analysis of the ovaries. The contemporary occurrence of postovulatory follicles and vitellogenic oocytes together in one ovary indicates that the studied species is a batch spawner. The high proportion of reproductive active females, their presence over the whole study time and the demonstrated OSFD of females indicate that E. punctifer is an indeterminate batch spawner. An extended spawning period of several months, or during the whole year, with possible bimodal intensity (not obligatory) is a character of an indeterminate serial spawning sh (George, 1998). Any time of the year a particular percentage of the anchovies is able to spawn. For this ability a constant biotic environment is necessary, which is the case in tropical coastal waters off West Sumatra. Serial spawners produce more eggs than a comparable (in size) total spawner. Small sh like anchovies usually do not have enough space in the body cavity, that would be necessary to keep the total amount of oocytes produced per year at the same time. The hydration of the oocytes has to be divided into portions (Lozan, 1985). The results of this study could be used as a contribution for estimating the stock biomass, using the egg-production-biomass (EPM), developed under the guidance of Lasker (1985) and brie y reviewed by Alheit (1993). Additional knowledge about the spawning grounds is important to quantify the effect of variation in prey density to spawning biomass and indirectly to recruitment. Tzeng and Wang (1992) found spawning areas for E. punctifer in a mangrove estuary in Taiwan. Their study gave a rst link that the standing stock of E. punctifer is affected not only by the shery impact, but also by the human utilisation of the mangrove estuaries and the variation in prey density. Acknowledgements We would like to thank Dr. A. Kunzmann for the support at the Bung Hatta University of Padang, West- Sumatra. Special thanks go to Dr. W. Ekau and two unknown reviewers for the critical review of the manuscript. Very special thanks go to the people of Pasir Kandang, without whose generosity and cooperation the entire work would not have been possible. References Alheit, J., Comparative spawning biology of anchovies, sardines, sardines and sprats. Rapp. P.v. ReÂun. Cons. Int. Explor. Mer. 191, 7±14. Alheit, J., Use of the daily egg production method for estimating biomass of clupeoid fishes: a review and evaluation. Bull. Marine. Sci. 53(2), 750±767. Adrianov, D.P., Lisovenko, L.A., Bulgakova, Yu.V., Oven, L.S., Reproductive ecology of the Black Sea anchovy (Engraulis encrasicholus ponticus): 1. Circadian rhythms of oogenesis and spawning. J. Ichthyology 36(7), 515±526. Bagenal, T.B., T. Methods for assessment of fish production in fresh waters. IBP Handbook No 3, 365 pp. Blaxter, J.H.S., Hunter, J.R., The biology of the clupeoid fishes. Adv. Marine. Biol. 20, 1±223. Beverton, R.J.H., Maturation, growth, growth and mortality of clupeid and engraulid stocks in relation to fishing. Rapp. P.v. ReÂun. Cons. Int. Explor. Mer. 154, 44±67. Clarke, T.A., Fecundity and spawning frequency of the Hawaiian anchovy or nehu, Encrasicholina purpurea. Fish. Bull. 85(1), 127±138. Dalzell, P., Some aspects of the reproductive biology of stolophorid anchovies from Northern Papua New Guinea. Asian Fish. Sci. 1, 91±106. Delsman, H.C., Fish eggs and larvae from the Java Sea. De Treubia 13, 217±242. George, M.R., Contributions to the use of condition factor: Studies of Spanish sardine, Sardinops sagax, and southern Pacific jack mackerel, Trachurus picturatus murphyi, off coast of Chile. ICES C.M. 1996/ H:4, p. 15. George, M.R., Die Fortpflanzungsbiologie zweier pelagischer Fischarten Sardinops sagax (Jenyns, 1842) (Clupeidae) und Trachurus picturatus murphyi Nichols 1920 (Carangidae) im Auftriebsgebiet Nordchiles. Biblothek Natur & Wissenschaft, Bd. 14, Verlag Natur & Wissenschaft, Solingen, 133 pp.

8 120 G. Maack, M.R. George / Fisheries Research 44 (1999) 113±120 Gerrits, P.O., Verfahren zur FaÈrbung von Gewebe, das in 2-Hydroxyethyl-Methacrylat eingebettet wird., 2nd ed., Sonderdruck fuèr Kulzer & Co GmbH, 31 pp. Grimes, C.B., Certain aspects of the life history of the vermillion snapper, Rhomboplites aurorubens, from North and South Carolina waters. Ph.D. Thesis, University of North Carolina, 240 pp. Hunter, J.R., Goldberg, S.R., Spawning indicence and batch fecundity in northern anchovy Encrasicholina purpurea. Fish. Bull. 77(3), 641±652. Hunter, J.R., Leong, R., The spawning energetics of female anchovy Engraulis mordax. Fish. Bull. 79(2), 215±230. Hunter, J.R., Macewicz, B.J., Lo, N.C.H., Kimbrell, C.A., Fecundity, spawning, spawning and maturity of female Dover sole, Microstomus pacificus, with an evaluation of assumption and precision. Fish. Bull. 90(1), 101±128. Lasker, R., An egg production Method for estimating spawning biomass of pelagic: application to the northern anchovy, Engraulis mordax. NOAA Technical Report NMFS 36, 99 pp. Lozan, J.L., Wachstum, Rekrutierung. Netzselektion, Fortpflanzung und Fruchtbarkeit. Fischereibiologische Methoden, Vol. III. Hamburg: Institut fuèr Hydrobiologie und Fischerei. Luther, G., Biology of whitebait anchovies of Indian waters. Tuna Baitfish in the Indo-Pacific Region. Proceedings of a Workshop, Honiara, Solomon Islands, pp.75±82. Parrish, R.H., Mallicoate, D.L., Klingbeil, R.A., Age dependent fecundity, number of spawnings per year, sex ratio, sex ratio and maturation stages in northern anchovy Engraulis mordax. Fish. Bull. 84(3), 503±517. Paula e Silva, R., Growth of the Bucaneer anchovy, Encrasicholina punctifer off Mozambique based in samples collected in research surveys. Rev. Invest. Pesq. Maputo (Mozambique) 21, 69±78. Rohdenburg, H., BeitraÈge zur Baganfischerei und zur BestandsabschaÈtzung von Encrasicholina punctifer (Engraulidae, Pisces) vor der KuÈste Padangs (West Sumatra, Indonesien). M.Sc. Thesis University of Bremen, Germany, 47 pp. Soesanto, V., Indonesian small-scale fisheries development. South China seafisheries development and coordinating programme, Manila, Philippines, 41 pp. Tiews, K., Ronquillo, I.A., Santos, L.M., On the biology of the anchovies (StolephorusLaceÂpeÁde) in Philippines waters. Proc. Indo-Pacific. Fish. Counc. 13(II), 20±48. Tzeng, W.N., Wang, Y.T., Structure, composition, composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River, Taiwan. Mar. Biol. 113, 481±490. Wright, P.J., The reproductive strategy of Stolephorus heterolobus in the South Java Sea. Tuna Baitfish in the Indo- Pacific Region. Proceedings of a workshop, Honiara, Solomon Islands, pp. 83±88. Wright, P.J., Ovarian development, spawning frequency, spawning frequency and batch fecundity in Encrasicholina heteroloba (Rupell, 1858). J. Fish. Biol. 40, 833±844.