STRUCTURE OF FISH COMMUNITY AND REPRODUCTIYE BIOLOGY OF THREE INDIGENOUS SPECIES OF CYPRINIDS IN KEDUNGOMBO RESERVOIR

The study investigated the structure of fish community and the reproductive biology of three indigenous species of cyprinids, namely Puntius goninnofas (Bleeker), Puntius bramoid.es (Cuvier & Valenciennes) and Myetacoleucus marginatas (Cuvier & Valenciennes) in the Kedungombo Reservoir, Central Java. Gillnet sampling in six sub-fishing areas of the reservoir once a month for a 12 month period was carried out. The structure of lish community was analysed descriptively. The study of reproductive biology included estimation of sex ratio, gonado-somatic index (GSI) and fecundity. Results showed that the fish community was composed of twelve species belonging to five families, i.e. six Cyprinidae species, three Cichlidae, one Channidae, one Bagriidae and one Clariidae. Five species, i.e. Oreochromis mossambicus, Puntiua gonionotus, Puntius bramoides, Mysta.coleucus margindtus and Channa strintus were dominant. These species were distributed all over the reservoir, except for C. striatus which was distributed in a specific area covered with grass and bushes. The highest value of species diversity and species richness occurred in the upstream portion of the reservoir. The riverine species which did not adapt well to the lacuetrine environment were concentrated in the dendritic riverine portion of the reservoir. Reproduction of P. gonianotus, P. brarnoides and M. m.argind.tus started from December until March when the water level of the reservoir began to rise. The sex ratios of the three indigenous species of cyprinids were not signiffrcantly different from 1: 1 (b0.05). Fecundity of P. gonionotue , P. bramoidcs and M. nxarginatus were between 25,980-86,916;42,454-99,659; and 4,702-15,681, respectively. The fecundity was positively correlated with total length, body weight, and gonad weight.


INTRODUCTION
Kedungombo Reservoir located in Central Java, Indonesia is a multipurpose reservoir, used for irrigation, hydroelectric power generation, flood control, fisheries and tourism.The dam was built across the Serang River and the area inun- dated in February 1990.The reservoir has a maximum surface area of 4.950 ha, a drawdown area of 1,750 ha, a maximum depth of 57 m and an average depth of 12.8 m.Based on its limnological characteristics, the reservoir was classified into mesotrophic lake (Krismono and Kartami-  hardja, 1990).r) flenmlmr nt the llnon,rrh Instltrrte for lrr.nlnvnlcr lrislx.r.ir\ Srrknnrn,ndi t0 Capture fisheries and aquaculture were prac- tised in the reservoir.The capture fisheries are dominant and are carried out by the people living in the vicinity of the reservoir.The development of capture fisheries and its management need the knowledge on biology and dynamics of the fish population.
The structure of fish community and their reproductive biology are primary aspects of fisheries biology.Fish species inhabiting a reser- voir form a community, the elements of which interact directly or indirectly.The pattern of interactions of individuals defines the organiza' tion or structure of a community or sub-commu- nity.Species diversity, equitability and dissimi' larity provide partial quantitative descriptions of communities or assemblages (Wootton, 1990).
The study on reproductive biology forms a basic part of the biology of fishes.Knowledge of the sex ratio and the state of maturity of individu- als in a population is useful, and estimates of fecundity are important in studies of population dynamics and productivity (Scott, 1979; Wootton,   1979).
The objectives of the present study are to investigate biological aspects of the fish community and the reproductive biology of the three indigenous species of cyprinids, Puntius gonio- notus, Puntius bramoides, Mystacoleucus marginatus in Kedungombo Reservoir.

Sampling Procedure
Gillnet fish sampling was adopted (FAO,   1975), to provide information on the structure of     The fleet of gillnets was set prior to sunset and lifted the next morning.The number of fish caught was recorded.The lengths and weights of fish were measured to nearest I mm and 5 g, respectively.The fish samples were dissected and the gut and the gonad were removed, labelled and preserved in 10% formalin.
Stretched Mesh Size (cm)

Structure of Fish Community
The analysis of the structure of the fish communities were based on the data of the experimental gillnet catches.The species diversity and richness were analysed descriptively.

Reproductive Biology
The sexual characteristics of the fish species were identified internally by observing their gonads.The ratio of female to male was tested statistically using Chi-square test.Sexual maturity of fish was based on the following method described by De Silva (1973):   stage I: immature, impossible to distinguish female from male macroscopically, II: unmistakably an ovary, very small.egg cells small, III: ovary fuller, eggs not yellow, IV: ovary full, almost fiUing body cavity, eggs yellow, V: ovary full, completely filling body cavity, eggs extruded under slight pressure on the belly, VI: a few yellow eggs, but ovary not full, wrinkled and reddish.
Gonado-somatic Index (GSI) is defined as the ratio of gonad weight to body weight expressed as t2 a percentage.The GSI and its variation over the 12 month sampling period were studied from females of maturity stage V. Fecundity (absolute fecundity) defined as the number of ripening eggs found in the ovaries of mature females (Bagenal, 1978) was also exam- ined.The fecundities of the three species were examined using a gravimetric method (Bagenal and Braum, 1978).The regression equation between fecundity and length of fish, fecundity and weight of fish, and fecundity and weight of ovary were constructed.

Structure of Fish Community
The fish from experimental gillnets consisted of twelve species (Table 2).
Table 2. List of fish species caught with experimental gillnets in the Kedungombo Reservoir. No.

Local Name
Scientific Name Family l.
The numbers of fish caught with gillnets according to sub-fishing areas ofthe reservoir are presented in Table 3.Based on the number of specimens caught, the distributions of Channa striatus, Mystus nigriceps, Clarias batrachus, Tylognathus hispidus, Cyprinus carpio and red tilapia were limited to specific areas.C. striatus was mainly found in areas with grass and bushes of sub-fishing areas III and Y. Mystus nigriceps.
T. hyspidus and C. batrachus were found in the upstream of the reservoir (the sub-fishing area I and VI), Cyrpinus carpio and red tilapia were found in the sub-fishing areas III, fV and V where the floating net cages culture exist.
The sub-fishing areas I, II, V and VI all had large number of O. mossambicus while the abundance of this species in sub-fishing areas III and [V was much lower.The sub-fishing areas I, II, V and VI were the upstream portions of the reservoir where the Serang and the Uter Rivers, still influence the environment.

Reproductiue Biology
In this study, the sex ratio of the three species were not significantly different from 1 : I (F0.05) (Table 4).
Figure 2 shows the gonado-somatic index according to the maturity stages.For all species, the GSI increased with the increasing maturity until stage V then it declined in the stage VL The GSI of spawning females, P. gonionotua varied from 2.95-15.83o/o. in P. bromoides 8.43-23.38o/o,and in M. morginafus 1.60-3.00%o (Table 5).The GSIs of females of the three species showed single peaks, being January for M. marginatus and March for the other two epecies (Figure  3).The GSI of females M. marginatue remained low, troughout the year.
Among the three species of cyrpinids, P.
bramoides had the highest absolute fecundity though M. marginatus had the highest relative fecundity (number of eggs/g of flesh).Firet maturity occurred at length of 16.5 cm in P. gonionotus,l5.5 cm in P. bramoides and 12.5 cm in M. marginatus.The relationship between fecundity and total length, body weight, and gonad weight are shown in

DISCUSSION
Fish in Kedungombo Reservoir were originally native species native to Serang river and its tributaries.Krismono and Kartamihardja (1990)  found eight native species inhabiting the Serang River and its tributaries.However, after the reservoir was impounded the fish composition t4 changed.In the present study, twelve species of fishes were caught.Four of these, i.e. C. carpio, O. mossambicus, O. niloticus and red tilapia were introduced species.Recently, five species, i.e.O. mossambicus, P. gonionotus, P. bramoides, M, rnarginatus and C. striatus are dominant although the latter is not important in the gillnet fishery.Although a riverihe fish fauna may be generally adapted poorly to the lacustrine envi-  Body Weight (W)   Gonad Weight (Gw)   Total Length (L)   Body Weight (W)   Gonad Weight (Gw)   Total l,ength (L)   Body Weight (W)   Gonad Weight (Gw)   logF= 2.7809 + 1.40841ogl ronment (Fernando and },Iolcik, 1982), several species in the Kedungombo Reservoir have adapted well.Four of the dominant species, namely O. mossarnbicus, P. gonionotus, P.
brarnoides and M. marginatus were distributed all over the reservoir.Those of the four species prefer to live in a lacustrine environment.Channa striatus was found in specific areas covered with grass and bushes where Rasbora orgyrotacnio and shrimp were abundant.Similar conditions were found in Kelang River, Malaysia where C. striatus was present in habitats with high densities of small cyprinid fishes (Mohsin  and Law, 1980).Wootton (1990) stated that the distribution of fish species is correlated with feeding habits and reproductive activities.The riverine species which could not adapt well to lacustrine environment such as Mystus nigriceps, Tylognathus hispidus and Clarias batrachus were concentrated in the dendritic part of riverine portion of the reservoir.Those of three species are known as a bottom living and they feed on bottom organism.
Sub-fishing areas I, II, and V have the higirer species diversity than the other areas (Table 3).
It was understood that sub-fishing areas I, II, and V were the areas rich in nutrients derived from the rivers and were mainly shallow.Eventhough sub-fishing area VI is also rich in nutrients and shallow, the area is more turbid compare to the areas I, II, and V. Therefore, the species diversity in the area VI is lower than the areas I, II and V.
Study on reproductive biology indicated that the sex ratios of the three species of cyprinids were not significantly different from l.It indicated that the mating system of the species can be categorize into a monogamy, mating partners remain together.The same sex ratios has also been noted in the cyprinid species, Barbus nigro- fasciatus, B. titteya, B. cumingi, B. bimaculatus and B. dorsalis (De Silva et aI., Ig85).The high- est fecundity occurred in P. bramoldes ranged fuom 42,454-99,659 eggs.The fecundity of M. marginatus was found similar to the described in earlier studies (Satria, 1991).The relationship between fecundity and total length, fecundity and weight, and fecundity and gonad weight showed that the fecundity increased with the increasing total length, weight and gonad weight.For all species, the best relationship was between the fecundity and gonad weight.It indicated that egg weight of the species were not highly varried.
Highest GSI was found in P. bramoldes female, denoting greater gonad weight.Changes in the GSI in relation to stage of maturity showed that pattern of variation in the GSI was similar for all species..The GSI seemed to increase from maturation stage I reaching up to the peak at maturation stage V.The GSI then decreased indicating a decrease in the gonad weight due to the release of the ova in the spawning season.The same pattern was also fqund in Puntius sarana (Chandrasoma   and De Silia, 1981).Wootton (19?9) sugested that such tropical species which have an extended breeding season with females spawning many times, show smaller changes in the amplitude of the GSI than those with a short season.Of the species presently investigated show greater changes in the amplitude of the GSI, suggesting that they would shed their eggs at once, individuals having a very short spawning period.Monthly variation of the GSI of P. gonionotus, P. bramoides, M. marginalus showed a single peak of the GSI occurring between December and March.This mean that spawning activity of P. gonionotus, P. bramoides and M. marginatus start in December when the water level began to rise and proceed until March.Similar spawning activity of cyprinids was found occurring in Jatiluhur Reservoir (Hardj amulia et aI., 1 988).

CONCLUSION
Management of habitat and fish population might be based on biological aspects investigated in this study.Spawning activity of the three indigenous species of cyprinids , P. gonionotus, P. bramoides and M. rnarginatus occurred in specific areas of the reservoir between December and March.According to these findings, regulation of fishing activities in specific areas could be beneficialand could include a closed season to protect spawning activities between December and March.

Fish
sampling was conducted systematically, once a month for 12 months at six sub-fishing areas ofthe reservoir (Figure 1).The fishing area I and VI are upstream and riverine with rela- tively high flow and eutrophic habitat.The fishing areas II and V represent a mixing area with a deeper basin, reduced flow and an intermediate trophic level.The fishing areas III and IV are lacustrine, little flow and an oligotrophic environ- ment.
Figure l.Map of the Kedungombo reservoir showing six sub-fishing areas,
Description of the gillnets IFR Journal Vol.II No.I.1996 fish community, distribution, composition, rela- tive abundance and length frequency distribution.Two fleets of monofilament floating gillnets were used.A fleet of gillnets consisted of nine pieces with different mesh sizes.Gillnets dimensions are summarised in Table l.

Table 6 . It Table 3 .
Number of fish species caught with gillnets in six sub-fishing areas over twelve months period.

Table 4 .
Sex ratio of mature specimen of the three indigenous fish species of Cyprinids in KedungomboReservoir.

Table 5 .
Gonado-somatic Index and fecundity of the three indigenous fish species of Cyprinids in Figure 2. Changes in gonado somatic index ini relation to stages of maturation in female Puntius gonionotus, Puntius bramoides and.My stacoleucus marginatus.