ISSN pending (print) PEERS Inc. Multidisciplinary Research Journal (Available at www.peersinc.org) ISSN 2546-0099 (online) Vol. 1, Issue 1, pp. 1-9, January-March, 2017 1 ESTIMATION OF THE EDIBLE WET TISSUE WEIGHT OF THE MANGROVE CLAM POLYMESODA EROSA HARVESTED FROM THE WILD Authors: Biona, Marvin A.; Marte, Clarisse R.; Pasadilla, Aimee Lou G.; Araneta, Bryan Yves G. ABSTRACT A technique on estimating the edible wet tissue weight of the common mangrove clam, Polymesoda erosa captured from the wild was established using Multiple Regression Analysis of five morphometric measurements namely, 1. Shell Length (SL), 2. Shell Width (SW), 3. Shell Height (SH), 4. Shell Volume (SV), and 5. Live Weight (LW). Pearson’s R showed highly significant correlations between the 5 estimating variables and Edible Wet Tissue Weight (WTW) indicating a strong link between them. Multiple Regression Analysis was not directly used to test for the best estimator because of the high correlation between the 5 independent variables. Instead, it was performed to create an estimation formula that will take into consideration all the contributions of the independent variables (SL, SW, SH, SV, and LW) to the estimation of the Edible Wet Tissue Weight. One-Way ANOVA at 0.05 level of significance however showed that there is a significant difference in terms of the contribution of the 5 estimator variables. B-values point to Shell Width and Shell Volume to have a significant contribution to the estimation formula. After considering all five estimators, the Edible Wet Tissue Weight of P. erosa can be estimated as follows: Estimated Wet Tissue Weight= -10.689 (constant) + (0.109 x SL) + (0.122 x SW) + (0.026 x SH) + (0.008 x LW) + (0.045 x SV). This study was able to demonstrate how Regression Analysis can be used to estimate the Edible Wet Tissue Weight not only of P. erosa but of all clam species especially those of commercial interest. Future interventions in clam artificial culture systems can use this because researchers cannot just open the clams and get initial base data and then return them again to culture tanks to continue the experiments. Estimations can be calculated without the need to sacrifice the organisms. Keywords: Polymesoda erosa, clam morphometry, wet tissue weight estimation INTRODUCTION The mud clam Polymesoda erosa is one of the edible bivalve species. They can be found in intertidal areas in mangrove mud and also in fresh and brackish waters of mangrove swamps, estuaries, and larger rivers. They are highly tolerant to surface desiccation of its habitat, can survive by aerial respiration for a period of a few days, and feed from subterranean water by means of water exchange through a narrow anterior gape of valves. Locally, it is called “tuway” by collectors in Sitio Lamintao, Barotac Nuevo, Iloilo, Philippines. Recently, the utilization of this bivalve species becomes famous due to its high protein content and delicacy in coastal areas (Norma and Norasma, 2016). Although it is not very popular in the Philippines because of the greater demand for the more favorite clam species, there have been several studies abroad that suggest its potential for mariculture (eg. Morton, 1984; Meehan, 1982; Lopez, 1988; Sarong et.al. 2015; Hamli et.al, 2014; and Rizal, 2016). There is P.A.L.G., M.C.R, B.M.A. Iloilo State College of Fisheries, Tiwi, Barotac Nuevo, Iloilo, Philippines, 5007 Corresponding Author: Bryan Yves G. Araneta, Iloilo State College of Fisheries, Tiwi, Barotac Nuevo, Iloilo, Philippines, 5007 [email protected] ISSN pending (print) PEERS Inc. Multidisciplinary Research Journal (Available at www.peersinc.org) ISSN 2546-0099 (online) Vol. 1, Issue 1, pp. 1-9, January-March, 2017 2 already plenty of literature on the various techniques and procedures in shellfish aquaculture. For species such as P. erosa, it would be best to culture them along mangrove areas via aquasilviculture- an environmentally friendly mangrove aquaculture program by the Bureau of Fisheries and Aquatic Resources (BFAR). One of the subtle issues surrounding shellfish culture is on the assessment of growth especially of the wet edible tissue. Unlike other cultured species where you can directly assess growth before and after introducing them to the culture system, clams can be a little tricky. Studying bivalve growth and establishing allometric relationships are essential for generating useful information for managing resources and understanding changing environmental conditions and pollution (Palmer 1990; Boulding and Hay 1993). Often growth is estimated by measuring shell dimensions or the volume of the animal (Deval, 2001), because they are simple, non-destructive methods that can be easily completed in the field. Once the allometric relationship is established, shell measurement is a sufficient surrogate to estimate biomass and total flesh production (Hibbert 1977; Rodhouse et al. 1984; Ross and Lima 1994; Thórarinsdóttir and Jóhannesson 1996; Ravera and Sprocati 1997). Shell measurements can be conveniently used to estimate biomass but in reality, consumers do not eat the shell. What matters is inside the shell- the edible wet tissue and more often by experience, consumers are disappointed by a large clam with very little inside or amazed by a medium-sized clam but is fully satisfying on the inside. It is thus critical to expect that shell dimensions will fail in estimating the flesh weight of an organism if not used carefully. Aquaculturists simply cannot remove the fleshy part of the clam for initial weighting and then return them to the culture tanks for future interventions and evaluations. At least in the experimental sense, it is a fact that it is hard to get baseline data in terms of edible wet tissue weight if the primary purpose of it is to culture the same animal to be assessed again at a later time. But theoretically, estimation is possible using the various shell dimensions (length, height, and width), shell volume, and live weight (shell + soft tissue inside). It is on this light that this study was conducted. METHODOLOGY This study utilized a Correlational Research Design. In this study, various measurements such as shell width, shell height, shell length, shell volume and live weight are tested if they are statistically associated with the edible wet tissue weight of P. erosa clam. One hundred eight (150) adult Polymesoda erosa clams ranging from 40-71 mm in shell length were bought from a local collector at Brgy. Tinorian, Barotac Nuevo, Iloilo, Philippines. They were cleaned and washed of sediments. They were transported and transferred to a 50-liter container containing artificial saltwater at 15ppt salinity in the Fisheries and Marine Science Lab of Iloilo State College of Fisheries, Tiwi, Barotac Nuevo, Iloilo, Philippines and were left overnight without food to clear their guts. Only 108 clams were used in the study. Too small and too large clams in the sample were not included as a contingency measure. The possibility that outliers will introduce errors in the analysis must be dealt with. Clams measuring lower than 20mm and greater than 90mm were removed as samples. Also very small clams have relatively very small fleshy tissue to be measured accurately. Shell length, height, and width were measured using Vernier calipers to the nearest 0.01mm. The shell volume was measured via simple displacement in a beaker with known volume of water initially measured using a graduated cylinder. Depending on the size of the clam, volume adjustments are done with extra water in a separate graduated cylinder. Before placing the clam in water, an initial volume is set. After the clam is submerged in the water the displaced volume is recorded. The empirical volume was also computed from the measured shell dimensions (LxWxH). If the clam is not fully submerged, an additional P.A.L.G., M.C.R, B.M.A. Iloilo State College of Fisheries, Tiwi, Barotac Nuevo, Iloilo, Philippines, 5007 Corresponding Author: Bryan Yves G. Araneta, Iloilo State College of Fisheries, Tiwi, Barotac Nuevo, Iloilo, Philippines, 5007 [email protected] ISSN pending (print) PEERS Inc. Multidisciplinary Research Journal (Available at www.peersinc.org) ISSN 2546-0099 (online) Vol. 1, Issue 1, pp. 1-9, January-March, 2017 3 measured volume is added. This method is more accurate than by simply calculating the empirical volume using the length x width x height measurements because the surface of the clam is obviously not uniform. Live weight was measured directly using a digital weighting scale to the nearest 0.01 grams. After sacrificing the animal, the fleshy tissue including the clam liquor (the fluid coming out of the fleshy tissue after scraping it from the shell) is also weighted in the digital scale. All measurements were encoded into Statistics Software and Multiple Regression Analysis was performed at 0.05 level of significance to determine the best predictor or estimate of edible wet tissue weight. Pearson’s Correlation was used to determine relationships between all the variables. Correlation analysis also justified the use of Multiple Regression Analysis because of the inferential nature of the investigation. The issue of multicollinearity among the predictor variables was ignored because all measurements were taken from the same individual organism and that is the reason why they are all correlated. The primary goal of this study is to construct a model equation where the contribution of each morphometric measurements to the estimation was established. There will be problems if there is no correlation between the predictor variables and the edible wet tissue weight. Since correlations are significant in this study, it supported the idea that Regression Analysis can be carried out for this purpose. RESULTS The following descriptive statistics came from all the measured shell dimensions, live weights and edible wet tissue weights of Polymesoda erosa in millimeters and grams respectively.