Gonad maturity of simping Placuna placenta, Linn 1758 (Bivalve: Placunidae) harvested from Kronjo Coastal, Indonesia

Simping Placuna placenta is a coastal resource found in shallow water with a muddy substrate. Simping widely used as a source of food and as raw material for the decoration. Utilization of simping until now has not yet focused on recruitment, reproductive aspect. This information is important as a basis data for determining the size of the simping catch. This study aimed to find out about of reproduction aspect, determining sex ratio the size of the catch simping. This research was conduct for three months at 3 locations. The number of samples in the analysis are 36 species to determine sex ratio and gonad maturity. Sex ratio indifferent from male and female, but based on the time sex ratio of simping significant, both male and female. The length size of gonads shellfish matures form 5.50 cm and 5.85 cm at 2nd maturity stage. Length of simping mature from 6.08 cm, 6.24 cm, 6.45 cm and 7.11 cm dominant at mature stage 3, and 8.61 cm dominant at 4 th maturity stage. Sex ratio of male and female are not significant between males and females (M: F=1;1). It is conculuded that the level of maturity of gonads is increasing as increases of size of simping.


INTRODUCTION
Simping (Placuna placenta, Linn 1758) is a bivalves group on the coastal area that has dual sexual or called as a hermaphrodite. Early cell development (larva stage) is difficult to explain the differences between male and female. Spawning generally occurs outside the body (external fertilization) (Le Pennec et al., 2003). Generally of mature simping at the adult stage of P. placenta at length more than 6 cm and spawning season in summer from April to May, or May to September. Gametes produced estimated that produced while spawning season between 15-21 million oocytes per spawning (Le Pennec et al., 2003). There are two types of spawning patterns of simping, first type adults stage spawn partially in the spring from April or May and reach peak season at the end of August (Mason, 1983). And the second type is for shells that have not to spawn previously will be spawning in the fall (from September to January) season.
The spawning season it is also followed by a period for gonad recovery for spawning the future. Gibson (1956) found a similar spawning pattern in the Bere island Ireland coast. At Bantry Bay, simping will return to mature gonads stage after six weeks from the spawning season. Spawning occurs outside the body; fertilization occurs in the water (Mason, 1983). After spawning, gonad development is the larval phase (pelagic larvae) for a month before settle in substrate. As a resource in coastal waters that have economic potential (as a source of protein and the economy) simping exploitation tends to simping degradation. The maintenance of simping production needed a strategy for increasing stock with aquaculture program. And in this study aimed to

Data collection
The sample collected was preserved on the polybag that has been labeled and preserved with formalin 10% and then analyzes in the laboratory. Laboratory activity is identifying of simping spat, pre-adult, and adult stage. Gonad maturity identifies from histology preparat from pre-adult and adult stage. Gonad preparation for histology preparat using Bouin's and alcohol 50%, 70%, 80%, 85%, 90%, 95%, and 100% alcohol, xylol, paraffin, solvents Hematoxylin and Eosin (HE).
High shell is measured by the distance dorsal to ventral maximum, using calipers with 0.01 mm accuracy. Shell height measurements carried out in Fisheries Biology Laboratory, Department of Aquatic Resource Management, Faculty of Fisheries and Marine Science, Bogor Agricultural University. Measurements of shells height needed to identify maturity level and the relationship with the development of the gonad size shells.

Sex ratio
Determination of sex differentiation based on gonad morphology and histology. If the color gonad orange means that female and color of the male is white. Ratio sex for male (m) higher than simping (female). Sex ratio simping shells can be seen in Table 2. Sex ratio of simping in each station are station 1 between 1, (F:M=5:1), station 2, F:M=0: 1) and at station 3 is (F:M=1.09:1). Statistical analysis (Chi-square) not significant (CL 95%) between simping males and females each station. That means simping sex ratio of (P. placenta) is proportional in the habitat with value is 1:1. Sex ratio analysis based on time of sampling found that sexual proportion in November Aceh Journal of Animal Science (2018) 5(1): 26-37 DOI: 10.13170/ajas.5.1.14930 29 http://jurnal.unsyiah.ac.id/AJAS dominant male (73 %), December 67%, but in January relatively stable. Statistical analysis between sampling time of simping sex ratio is different (significant at CL 95%).  Figure 2. The sex ratio of male and female shell on the station

Gonad maturity
Ganad maturity is the reproductive phase of gonad to produce their new generation and sustain their population in the habitat. Simping size more than 5 cm, gonad maturity classified bay morphology technique, but less size must be use histology. Gonad histology of simping population and its cell content explain in Figure 3. Gonad anatomy performance began filling the posterior gonad organs (viscera) to the interior side by side with digestion. A female gonad is yellow and older than male gonad. The gonads edge directly adjacent to the shell and the posterior part. Female gonads edges have a thin labial attached to the edge of the shell. Gonad morphology before preservation looks slightly yellowish gradually faded. However, while research did not find a hermaphrodite shell.
Morphology analysis found that the first time of simping maturity at length sizes more than 6 cm. Shells have genital simping separate (dioecious), gonad sex mature female orange, and male gonads mature sex is white. Determination of shellfish simping gonad maturity stage studied based on image analysis of gonad histology preparations -the result of gonad maturity, as shown in Table 3.  In the cavity, eggs partially occupied mature or immature eggs. Cavity eggs more developed bigger than before the stage. 6.24 cm 3b Volume eggs cavity bigger, and partially eggs develop in the cavity cell body. 6.45 cm 3c Eggs adhere to body cell and more develop that before the stage. Eggs color more clearly and male or female separate. 7.11 cm 3d Mature cell egg cavity, each cell fills up, and nucleus eggs visible. Cel cavity that fulfills of mature has the form eclipse and nucleus. All of the cavity cells fulfill by mature eggs. And then also found mature eggs without a nucleus cell.

cm
Spawning stage 4a The whole body cavity fulfills by mature eggs. In eggs with having nucleus, cell growth up better, but also found an empty cell. In this stage, the assessing spawning process begins. Maturity size close relate with length and weight of Simping. Simping sizes that observe histology are 5.50 cm and 5.85 cm for maturity stage 2 (developing). Simping shell size 6.08 cm, 6.24 cm, 6.45 cm, and 7.11 cm for maturity stage 3 (ripe), and shell size was 8.61 cm for maturity stage 4 (spawn). Gonad development each stage of simping seen in Figure 4. Based on figure 4 can be seen that the shells simping stage 2 in the developing stage. At this stage, we found the cavity follicle undeveloped in better conditions. Most of the eggs cell in cavity an immature condition (Figure 4.a). At maturity stage 3, gonad condition has been maturing (ripe). The entire cavity cell consist of mature eggs (oocyst) cell, the nucleus of eggs develop, and identified ( Figure  4.b). Gonad maturity stage 4, egg cell prepare for spawning season. The oocyst has been issue by the cavity, and part of follicle cavity began empty from the end of December (Figure 4.c).

DISCUSSION
Water quality status at the research site was suitable for biota growth and development. Simping larva, pre-adult and adult high abundance at clear waters with TSS levels between optimum 0-20 mg/ l (Lee et al., 1978in Bahtiar, 2005. According to Dharmaraj et al. (2004) growth optimal in the range of salinity between 18-38 pro mill and optimum pH from 6.4-7.7.
Environmental parameter suitable for biota and ecosystem except chemical oxygen demand tends higher than the standard value. The accordance of Minister of Environment No 51/2004No. 115/2003 regulations for water quality, where relatively in good condition and suitable for biota. In Virginia, estuary average monthly of temperature within 1-2 o C each other salso stimulate of mollusk reproduction respond (Harding et al., 2012). Ceure and Boehs show in Cachoeira (2012) river effect of salinity to gamete release in the water body. Rhine River also seems to increase stress response after stimulating by temperature and indirectly increasing the mortality rate (Petter et al., 2014). In general, the distribution of P. placenta, influenced by environmental conditions. Most of the benthic studies influenced by physicochemical, biological characteristics explored that Glycera is the dominant species in prevailing in the environment Varadharajan (2010), which has been a greater influence in April (Yonvitner et al. 2010).
Generally, the proportion male higher than females at the end of the year. This condition different from Anadara antiquates in Pakistani, where the population dominantly in mature and significant to evaluate sex ration (Jahangir et al., 2014). The sex ratio analysis is needed to ensure the sustainability of the recruitment process. Not only environment status, the success of the recruitment process depends on the sex ratio of adult stock. Others sessile species that have similarly character such as A. granosa (Narasimham, 1998); A. tuerculosa with sex ration 1:1 (Cruz et al., 1984); A. inaequivalvis 1.04-1 (Sahin et al., 2006) and P. placenta (1: 1).
In April, when the surface water temperature reached 17°C, 6.3% of the female oysters and 37.5% of male oysters were at an early development stage, exhibiting early vitellogenic oocytes and spermatogonia (Kim et al., 2010). Food supply in this period that used the amount of carbohydrate at a minimum (Shafakatullah, 2013). Different from Mytilus edulis, that substrate in the water column, more active in sorting particle while spawning period (Espinosa and Allam, 2013). Shell population which was highly abundant in the and more tourists (December-February). Santos and Boehs (2011). In case Clams from Ria de Aveiro seem to have 435 the ability to recover the reserves quickly after spawning when the SST and food 436 availability (chlorophyll) are still high (Matias et al., 2013) Length and age-classes (Table 2) were significantly different from 1:1 only in Groups 1 and 3 (Harding et al., 2012). Maturity size close relate with length and weight (Avila-Poveda et al., 2009), where simping sizes that observe histology are 5.50 cm and 5.85 cm for maturity stage 2 (developing). According to Dharmaraj et al. (2004), simping shellfish reach adulthood when length