Growth and condition index of pokea clams ( Batissa violacea var. celebensis , von Martens 1897) in Lasolo River Mouth, Southeast Sulawesi

. The somatic growth and condition index (CI) of pokea population aren’t yet fully known in the Lasolo river. This research aims to decide the somatic growth relationship between length and weight as well as the condition factor of pokea population. This research was carried out in the Lasolo river from January-December 2014. Pokea clams were taken from the river bed with traditional tool ( tangge ). The length and total weight of the clams were determined by employing a caliper with a precision of 0.5 cm and a digital scale with an accuracy of 0.01g. Meat and shells were then dried in an oven at 70 o C about 48 hours. The dry weight of the meat and the shells of the pokea clams were weighed using a digital scale with an accuracy of 0.0001 g. Calculations obtained average b parameter values of the males and females about 2.52 and 2.70, respectively. The b values for both sex of clams were 2.37-3.05 and 2.24-3.15, respectively, which were within the negative allometric category. The CI values of the male (3.98±1.44) and female (4.27±1.52) putting them in the fat category. The condition index experienced three local peak periods in February-March, June, and November-December.


Introduction
Pokea clams are freshwater clams that inhabit river mouths and can be found in the majority of large rivers in Southeast Sulawesi.These rivers include the Langkumbe river, Laeya river, Pohara river, and Lasolo river [1] .These freshwater clams possess important economic value and have thus been cultivated by fishermen.It has been reported in Pohara river that the commercial production rate of pokea clams is 155 tons per year and it fall under the overexploited category with an E value of 0.69 [2] .
To maintain their population in nature, organisms, including pokea clams, may adapt reproductive strategies, for instance, through faster and rapid growth into adult/mature age [2] [3] .Pokea clams have a fast regeneration cycle, which is indicated by the early gonad maturity that occurs at a small size of 2.3 cm, the occurrence of 2 spawning peaks within a year, as well as the partial spawning that lasts for 7 months [4] .Intensive exploitation of pokea clams within the Lasolo river estuary, especially targeting larger-sized clams with substantial biomass, has the potential to lead to a reduction in clam growth.This can be discerned through the assessment of the length-weight (LW) relationship and the condition index (CI) of the clam population.
Studies on pokea clams have been carried out, including the clam reproduction in the Laeya river [5] and Lasolo river [2] , density and distribution in the Pohara river [1] , dynamics and population growth in the Lasolo river [4][3] , as well as morphometric characteristics in the Pohara river [6][7] .However, the study of Batissa in the Lasolo river estuary has yet to be done, especially their growth and condition index.This study aims to assess the growth of clam species in the Lasolo river, Southeast Sulawesi, through their LW relationship and CI.

Research methodology 2.1 Procedure
The present study was carried out for a year in January-December 2014 in the Lasolo river.Pokea clam samples were extracted from four sampling sites covering the entire area whereby the clams were first found upstream and nearing the estuary (Fig. 1).Clam samples were collected using local traditional fishing gear, known as tangge (basket).This basket has a mouth opening diameter of 20 cm.The fishing gear was maneuvered in the direction of the water flow and lifted to the surface.The sampled clams were counted, then the shell length is measured using a caliper (accuracy of 0.5 mm), then weighed by a digital scale (accuracy of 0.01 g) (Fig. 2).The clam samples were brought to the laboratory and it is divided by sex build upon the color of the gonad, whereby male clams have milky white color and female clams have a yellow to brown color.The clams were then dried using an oven for 48 hours at 70 o C to obtain the dry weight of the shell and the meat.The shells and meat of the clams were then weighed using an analytical balance with an accuracy of 0.0001 g.

Data analysis
The investigation of the LW relationship of the clams was entailed employing the equation advocated by the author cited as [8] :  =   (1) where: W = fresh weight (g); L = shell length (cm); a and b = constants The constants a and b were obtained from the linear regression equation as follows: Log W = log a + b log L (2) The condition index of pokea clam was analyzed by the equation suggested of [9][10] : where: CI = condition index, dmw= dry meat weight (g); dsw = dry shell weight (g) descriptions: <2= thin; 2-4 = moderate; and ≥4 = fat.

Length-Weight relationship
The b values of the both sexes of the clams in the Lasolo river were in the range of 2.37-3.05and 2.24-3.15,respectively.The average of b values of all the males and females were below 3.0 with their respective values of 2.52 and 2.70.Temporally, the b values of the males and females showed similar patterns, whereby they exhibited increases in February-March, May-July, September-October, and December (Tab.1,Fig. 3).Moreover, the R data, 2022).The pokea clams of the Lasolo river are taking to those in other rivers with clams having b values of less than 3.0 [8] such as the Pohara river with a range of 2.29-2.56 [11]and the Laeya river of 2.61 and 2.78 (Unpublished data, 2022).The value of the b parameter varies based on the time of observation [11] and tends to synchronize between the males and the females (Unpublished data, 2022).In the present study, the b value experienced increases in February-March, May-July, September-October, and December.These increases (b value) can be attributed to factors such as 1) the increase in weight of clams during the development process to reach peak gonad maturity [4] [12] , 2) the food availability on the river bed and their high conversion into meat or muscle [13] .The low b value of Batissa clams in the Lasolo river can be assumed to be the result of the high exploitation of the clams, which favors clams of larger size and meat quantity.The high exploitation would cause a shift in the size of clams available in nature to smaller sizes, thus producing low b values [7][14] .

Condition index
The CI values of pokea clams obtained for male about 3.98±1.44and female about 4.27±1.52.The Mann-Whitney U test conducted at a significance level of  = 0.05 yielded nonsignificant results, indicating that there were no statistically significant differences observed in the CI between both sexes of specimens of that clams, as illustrated in Figure 4. Based on size groups, the CI of both sexes of Batissa clams in the Lasolo river showed similar trends, whereby the condition index value would increase up to the shell size of 5.50 cm.The peak of the condition index occurred at the size of 3.51-4.00cm and it decreased beyond the size of 5.50 cm.The temporal trends of the condition index of the both sexes of the clams were similar, they reached their peak in February-April, June, and November-December (Fig. 5).The CI values of the male (3.98±1.44)and female (4.27±1.52)pokea clams demonstrated that the clams were of the medium to fat category [15][16] .The pokea clams in Lasolo river were able to maintain themselves because 1) as an estuarine species, pokea clams can consume organic matter and plankton available on the river beds through their filter feeding [17] and pedal feeding [18] mechanisms, which allow pokea clams to have a high productivity [19][3] , and 2) the Lasolo river receives supplies of nutrients from fertile soil upland, which is highly favorable for the growth of the clams [3] .
The male and female pokea clams experience an increase in condition indices from their infant to the size of 5.50 cm.The CI value reached its peak at the size of 3.51-4.00cm and decreased in clams with a size > 5.50 cm.A high CI value at this size indicated a productive phase in which the clams were able to utilize food and converted them into body tissues.This was also illustrated in the length-weight relationship, whereby there were inflection points that showed a greater change in weight at a certain length.This occurrence implied an increase in the somatic growth of clams to a size of 5 cm which would then decrease at the size of > 6 cm [3] .
The condition index of the both sexes of the clams showed relatively similar patterns with local peaks in February-April, June, and November-December.The increase or decrease in the condition index of clams can be related to spawning behavior [20][21] .The developmental or maturation phases of the gonads typically produce an increase in the condition index as a result of yolk accumulation and increasing egg size.Moreover, the decrease in the condition index can be caused by the decrease in the number of eggs after spawning, followed by a reproductive resting phase.In the case of Batissa clams in the Lasolo river, the gonad maturity development began in January, followed by a peak in the gonad maturity which occurred in April, and then spawning in May.The pokea clams also experienced partial spawning, with a secondary peak gonad maturity occurring in June and spawning at the end of July to October.Partial spawning was found to have occurred in April and May until the end of spawning in October [4] .Additionally, the condition index also experienced increases in January-February, which was the beginning of gonad development, and November-December, which was when the resting phase took place.Clams carry out somatic development after spawning which is characterized by the high availability of food (organic matter and chlorophyll a) [3] .

Table . 1
. Temporal shell LW relationship of Batissa clams in the Lasolo river The total shell LW relationship of Batissa population in the Lasolo river The b parameter values of the male and female pokea clams were 2.52 and 2.70, which indicated that the clams had negative allometric growth.The b parameter of Batissa clams in the Lasolo river was similar to the Batissa clams in the Pohara river, with males ranging from 1.87-2.78and females ranging from 2.09-2.82,as well as the Batissa clams in the Laeya river with males ranging from 2.45 to 3.03 and females ranging from 2.45 to 2.94 (Unpublished