Research Article |
Corresponding author: Ricardo P. Babaran ( rpbabaran@upv.edu.ph ) Academic editor: Sanja Matić-Skoko
© 2024 Cheryl Jela, Harold M. Monteclaro, Nathaniel C. Añasco, Gerald F. Quinitio, Ricardo P. Babaran.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Jela C, Monteclaro HM, Añasco NC, Quinitio GF, Babaran RP (2024) Identification of pen shells (Bivalvia: Ostreida: Pinnidae) collected off northern Iloilo, Philippines using their morphological characters. Acta Ichthyologica et Piscatoria 54: 49-61. https://doi.org/10.3897/aiep.54.112465
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This study describes morphological characteristics of pen shells collected along the coast of northern Iloilo, Philippines. A total of 380 pen shell individuals with intact shells and their adductor muscles were carefully examined and measured. Eleven species were studied, namely: Atrina pectinata (Linnaeus, 1767), Atrina inflata (Dillwyn, 1817), Atrina vexillum (Born, 1778), Atrina seminuda (Lamarck, 1819), Atrina rigida ([Lightfoot], 1786), Pinna bicolor Gmelin, 1791, Pinna atropurpurea Sowerby, 1825, Pinna deltodes Menke, 1843, Pinna muricata Linnaeus, 1758, Pinna incurva Gmelin, 1791, and Pinna nobilis Linnaeus, 1758. The species were identified based on the nine characteristics of the valve for the genus Pinna and eight for the genus Atrina. These characteristics were then correlated with their adductor muscles’ morphology. Analysis of variance revealed that the three most dominant species investigated under genus Atrina, namely Atrina pectinata, Atrina inflata, and Atrina vexillum, were found to be significantly different in the eight characters of the valve (P < 0.05). Moreover, three representative Pinna species, Pinna bicolor, Pinna atropurpurea, and Pinna deltodes, were significantly (P < 0.05) different based on shell width, dorsal posterior shell margin, sulcus width, and dorsal posterior margin to dorsal nacreous margin. The observed high correlation (P < 0.05) between adductor muscle properties and different shell length characteristics for five dominant species can be used as a predictor of growth and suggests that the increase in the size of adductor muscle correlates to the increase in the size of the mentioned shell characteristics. No previous study of this kind was conducted in the Philippines. This work provides relevant information for related biological research on other pen shell species and for the management of pen shell resources in northern Iloilo and, possibly, other regions in the world.
adductor muscle, Atrina pectinata, fisheries management, growth predictor, Pinna bicolor, taxonomy
The family Pinnidae (Order: Ostreida) belongs to the class Bivalvia and is commonly known as pen shell (
Morphologically, pen shells are cryptic (
Aside from northern Iloilo, other active fisheries for pen shells are localized in various areas in the Philippines, but the species of interest is always Atrina pectinata (Linnaeus, 1767) because of the high demand for its adductor muscle by the export market, particularly in Taiwan. Each year about 20 tonnes of this species are captured by local divers in the southwestern region of the Visayan Sea (
Pen shells have a large posterior adductor muscle that is responsible for the opening and closing of the shell. It appears as dark and light phases, which are respectively called blocking and working muscles (
In managing wild pen shell resources, it is important to make an accurate identification of species occurring in a certain locality. Previously,
Obtaining morphological data of pen shells at the landing sites is not possible due to the existing fishing method, which requires underwater extraction of the meat each time a pen shell is encountered. With the aid of a compressor, divers extract individual pen shells from their habitat, shuck all the meat, and leave empty shells at the sea bottom. This method is preferred because more meat can be collected during each dive. Moreover, the shells are no longer loaded on their small boats because of their bulkiness. Also, there is no motivation for landing the shells because there is no market for them. Therefore, categorization of species monitoring based on shell shape and size is not possible. However, it was observed that the adductor muscles landed at local markets with their mantle have different shapes. Thus, an alternative morphological characterization strategy based on the shapes of the adductor muscles can be adopted. The information obtained would provide insights as to which species need to be managed. More detailed measurements of their morphological characteristics would also provide information about pen shell diversity in the area.
This study focuses on species of the family Pinnidae. First, it aims to update the checklist of Atrina and Pinna species that occur in the coastal waters of the Visayan Sea, off northern Iloilo, in the Philippines. This information is useful for future research related to the taxonomy, morphology, and genetic diversity of pen shell species in the Philippines. The second objective seeks to determine some relations in the characters of landed adductor muscles and the pen shells, which may be used for identifying species for better management.
Study area. This study was carried out in the coastal waters of northern Iloilo, part of the Visayan Sea, Philippines (Fig.
Sample collection and measurements. A total of 380 intact adult individuals of various pen shell species were collected using compressor diving, stored in a styrofoam box, preserved with ice, brought to the biological laboratory of Northern Iloilo State University, and carefully examined for morphological measurements and identification. The specimens were cleaned with a metal knife to remove epibionts and washed with tap water to remove dirt. Shells were carefully shucked individually and flesh was removed. The right valve of each shell was measured using a Vernier caliper to the nearest 0.01 mm following the method of
The measurements are not the same for all species because of varied morphologies. It is important to note that the dorsal posterior shell margin differs in Atrina and Pinna species. Measurement of nacreous length started at the end of the muscle scar because the nacreous layer was apparent at the end of the posterior margin of the anterior adductor muscle scar. Moreover, for species of the genus Pinna, the sulcus width was also measured (Fig.
A diagram of the interior right valve of genus Pinna (A) showing the position of the nacreous layer and 8 characteristics of the shell. 1 = total shell length (TSL); 2 = length of anterior to posterior adductor margin (LAPAM); 3 = posterior adductor to posterior shell margin (PAPSM); 4 = dorsal posterior shell margin (DPSM); 5 = dorsal margin (DM); 6 = shell width (ShW); 7 = sulcus width (SuW); 8 = posterior adductor margin to posterior nacreous margin (PAMPNM) and 9 = dorsal nacreous length (DNL). A diagram of the interior right valve of genus Atrina (B) showing the position of the nacreous layer and 8 characteristics of the shell. 1 = total shell length (TSL); 2 = length of anterior to posterior adductor margin (LAPAM); 3 = posterior adductor to posterior shell margin (PAPSM); 4 = dorsal posterior shell margin (DPSM); 5 = dorsal margin (DM); 6 = shell width (ShW); 7 = posterior adductor margin to posterior nacreous margin (PAMPNM); and 8 = dorsal nacreous length (DNL).
Species identification. The specimens were identified based on their morphological characteristics such as shell structure, specifically in the way the parts are organized, and sculpture, as indicated by length, color patterns, and other related traits. Identification guides include the works of
Data analysis. The mean and standard deviation of the different shell and adductor muscle morphometric characters were calculated for each species. One-way analysis of variance was used to estimate the differences in the means of the different parameters of the shells. Post-hoc tests were subsequently applied to show how the various parameters differed. This analysis was performed using the SPSS package, ver. 20. Before analysis, the normality of data was tested using the Kolmogorov–Smirnov test. Using three dominant species of the two pen shell genera in this study, the relation between shell and adductor muscle morphology was determined by linear regression.
Five species of the genus Atrina, namely, Atrina pectinata, Atrina inflata (Dillwyn, 1817), Atrina vexillum (Born, 1778), Atrina seminuda (Lamarck, 1819), and Atrina rigida ([Lightfoot], 1786) and six species of the genus Pinna, namely, Pinna bicolor Gmelin, 1791, Pinna atropurpurea Sowerby, 1825, Pinna deltodes Menke, 1843, Pinna muricata Linnaeus, 1758, Pinna incurva Gmelin, 1791, and Pinna nobilis Linnaeus, 1758 were collected from the waters of northern Iloilo. Table
Principal metric shell characters of eleven pen shell species of the genera Atrina and Pinna (family Pinnidae) based on literature sources.
Species | n | Metric shell character [mm] | ||||||||
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TSL | LAPAM | PAPSM | DPSM | DM | ShW | SuW | PAMPNM | DNL | ||
A. pectinata 1 | 55 | 199.95 ± 47.07 | 106.57 ± 30.91 | 72.92 ± 18.75 | 52.56 ± 33.37 | 181.40 ± 40.70 | 93.16 ± 27.27 | 0.00 | 8.06 ± 1.51 | 125.95 ± 27.95 |
A. inflata 2 | 47 | 164.40 ± 25.27 | 94.61 ± 14.40 | 61.08 ± 14.39 | 92.21 ± 35.40 | 131.12 ± 20.02 | 101.54 ± 17.88 | 0.00 | 3.11 ± 1.74 | 107.90 ± 16.94 |
A. vexillum 2 | 17 | 173.45 ± 33.87 | 96.37 ± 21.47 | 55.51 ± 14.57 | 70.76 ± 24.57 | 117.66 ± 17.21 | 115.76 ± 22.09 | 0.00 | 0.00 | 101.55 ± 16.50 |
A. seminuda 3 | 1 | 274.00 | 138.00 | 102.00 | 29.00 | 219.00 | 161.00 | 0.00 | 19.00 | 162.00 |
A. rigida 3 | 1 | 240.00 | 140.00 | 45.00 | 115.00 | 160.00 | 145.00 | 0.00 | 0.00 | 145.00 |
P. bicolor 2 | 43 | 299.10 ± 50.12 | 137.30 ± 27.79 | 122.61 ± 20.95 | 41.43 ± 5.38 | 251.37 ± 48.79 | 98.80 ± 17.35 | 2.37 ± 0.47 | 4.73 ± 1.92 | 157.59 ± 29.25 |
P. atropurpurea 2 | 34 | 293.87 ± 39.58 | 135.20 ± 20.97 | 121.55 ± 15.18 | 50.54 ± 4.45 | 248.03 ± 38.11 | 122.4 ± 7.84 | 4.94 ± 0.78 | 7.56 ± 4.49 | 158.02 ± 31.80 |
P. deltodes | 10 | 280.18 ± 93.34 | 142.71 ± 32.36 | 131.42 ± 18.80 | 89.58 ± 45.10 | 269.29 ± 41.35 | 120.95 ± 15.76 | 9.10 ± 0.94 | 9.38 ± 0.67 | 177.44 ± 49.58 |
P. muricata 2 | 2 | 225.50 ± 0.71 | 109.50 ± 9.19 | 102.00 ± 2.83 | 54.00 ± 8.49 | 223.5 ± 4.95 | 123.50 ± 10.61 | 4.00 ± 0.00 | 2.12 ± 0.18 | 135.50 ± 27.8 |
P. incurva 5 | 1 | 257.00 | 93.00 | 130.00 | 31.00 | 240.00 | 96.00 | 1.00 | 5.00 | 122.00 |
P. nobilis 6 | 1 | 419.00 | 172.00 | 205.00 | 93.00 | 365.00 | 133.00 | 8.00 | 14.00 | 223.00 |
Descriptive characters of eleven pen shell species of the genera Atrina and Pinna (family Pinnidae) based on literature sources.
Species | Description/Comment | Reference |
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A. pectinata | Large, thin, fragile, and triangularly wedge shaped; shell external surface slightly shiny, light-tannish grey tinged with brownish toward the umbone |
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A. inflata | Strongly swollen shape shell |
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A. vexillum | Dark to almost black color of shell |
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A. seminuda | Large, fan-shaped, and triangular with 15 narrow radial ribs separated by larger interspaces | Leal 2008 |
A. rigida | Large, triangular in shape, and surface of shell with 15 radial ribs |
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P. bicolor | External valve of shell dark purple with nearly straight ventral margin and dorsal margin |
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P. atropurpurea | External valve of shell dark purple; ventral margin and dorsal margin nearly straight |
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P. deltodes | Shell length reached up to 370.8 mm; dorsal and ventral regions flared posteriorly and nearly rounded at apex with highest point between dorsal and ventral margins | Scheltema 1983 |
P. muricata | Triangulated, whitish in color, blotch of dark purple | Winkworth 1929 |
P. incurva | Narrowly attenuated shell; light yellow at posterior and reddish-brown towards anterior | Stella et al. 2015 |
P. nobilis | World’s largest triangular-shape bivalve |
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Photographs of selected species of the genus Atrina showing the external and internal surface of the right valve collected from northern Iloilo, Philippines. External valve (A.1, B.1, C.1, D.1, E.1), internal valve (A.2, B.2, C.2, D.2, E.2). Atrina pectinata (A.1–A.2), A. vexillum (B.1–B.2), A. inflata (C.1–C.2), A. seminuda (D.1–D.2), and A. rigida (E.1–E.2).
Photographs of selected species of the genus Pinna showing the external and internal surface of the right valve collected from northern Iloilo, Philippines. External valve (A.1, B.1, C.1, D.1, E.1, F.1), internal valve (A.2, B.2, C.2, D.2, E.2, F.2). Pinna bicolor (A.1–A.2), P. deltodes (B.1–B.2), P. atropurpurea (C.1–C.2), P. incurva (D.1–D.2), P. nobilis (E.1–E.2), and P. muricata (F.1–F.2).
Differences in shell morphology of dominant species. Only the dominant species were used to compare the shell morphology of pen shell species. These include three species of the genus Atrina, namely, A. pectinata, A. inflata, and A. vexillum, and three species of the genus Pinna, namely, P. bicolor, P. deltodes, and P. atropurpurea. These were subjected to length–length analysis. The other species were not analyzed because the number of specimens for them was inadequate. Figure
Measurements of eight morphometric characters of Atrina inflata (n = 45), A. pectinata (n = 231), and A. vexillum (n = 17). Values are expressed as the mean ± standard deviation. TSL = total shell length (A), LAPAM = length of anterior to posterior adductor margin (B), PAPSM = posterior adductor to posterior shell margin (C), DPSM = dorsal posterior shell margin (D), DM = dorsal margin (E), ShW = shell width (F), PAMPNM = posterior adductor margin to posterior nacreous margin (G), DNL = dorsal nacreous length (H). Small letters above the columns indicate the results of post-hoc tests.
Measurements of nine morphometric characters of the genus Pinna: P. bicolor (n = 43), P. atropurpurea (n = 34), and P. deltodes (n = 10). Values are expressed as the mean ± standard deviation. TSL = total shell length (A), LAPAM = length of anterior to posterior adductor margin (B), LPAPSM = length of posterior adductor to posterior shell margin (C), LDPSM = length of dorsal posterior shell margin (D), DM = dorsal margin (E), ShW = shell width (F), SuW = sulcus width (G), PAMPNM = posterior adductor margin to posterior nacreous margin (H), DNL = dorsal nacreous length (I). Small letters above the columns indicate the results of post-hoc tests.
Adductor muscle morphology. Representative specimens of the posterior adductor muscles of the most dominant species belonging to the genera Atrina (Fig.
Selected biometric characters of the adductor muscle of five pen shell species of the genera Atrina and Pinna (family Pinnidae) collected from northern Iloilo, Philippines.
Species | n | Biometric characters | Descriptive characters | ||
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AMW [g] | AMT [mm] | AML [mm] | |||
A. pectinata | 53 | 7.99 ± 5.30 | 13.52 ± 5.68 | 21.13 ± 8.04 | Fibers smooth, packed with epithelial tissue with no fissures and cavities. Most of muscle comprised of dark muscles |
A. inflata | 47 | 7.47 ± 4.55 | 17.30 ± 3.45 | 24.42 ± 6.31 | Tubular-like, asymmetrical, dark muscle 57.14 percentage points thicker than light muscle, light muscle attached to dark muscle by epithelial tissue, longitudinal fissure easily recognizable at external side of surface of adductor muscle |
A. vexillum | 17 | 12.61 ± 10.59 | 14.81 ± 6.26 | 24.25 ± 9.30 | Shape nearly circular, fibers packed with yellow epithelial tissue, comprised of high percentage of dark muscles, fissures, and cavities observed in muscles |
P. bicolor | 43 | 11.52 ± 4.35 | 12 ± 4.57 | 19.46 ± 8.54 | Fibers well packed with thick epithelial tissue. |
P. atropurpurea | 34 | 11.82 ± 4.95 | 14.24 ± 4.81 | 22.20 ± 4.87 | Dark muscle occupying almost half of total area, fissures visible in light muscles |
Relation between shell length characters and adductor muscles of dominant species. The regression equations between the different length characteristics and their respective adductor length and thickness for five dominant pen shell species (r2, 0.23–0.94) are shown in Table
Relations of thickness (AMT) and length (AML) of adductor muscles with various shell length characters of five pen shell species of the genera Atrina and Pinna (family Pinnidae) collected off northern Iloilo, Philippines.
Species | Shell length parameter | Regression equation in relation to AMT | r 2 | Regression equation in relation to AML | r 2 |
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A. pectinata | TSL | TSL = 118.18 + 6.1775AMT | 0.65 | TSL = 115.12 + 3.6141AML | 0.70 |
LAPAM | LAPAM = 64.95 + 3.7165AMT | 0.68 | LAPAM = 57.0798 + 3.6865AML | 0.53 | |
PAPSM | PAPSM = 50.933 + 1.6319AMT | 0.49 | PAPSM = 48.9457 + 1.1068AML | 0.40 | |
DPSM | DPSM = 16.455 + 0.5544AMT | 0.53 | DPSM = 15.588 + 0.3827AML | 0.46 | |
DM | DM = 113.62 + 5.2092AMT | 0.62 | DM = 102.35 + 3.7313AML | 0.55 | |
ShW | ShW = 42.959 + 3.7025AMT | 0.68 | ShW = 38.45 + 2.5204AML | 0.60 | |
PAMPNM | PAMPNM = 5.9356 + 0.1743AMT | 0.57 | PAMPNM = 5.6912 + 0.12AML | 0.50 | |
DNL | DNL = 79.162 + 3.5137AMT | 0.63 | DNM = 82.243 + 3.4853AML | 0.55 | |
A. inflata | TSL | TSL = 38.411 + 7.2823AMT | 0.94 | TSL = 77.9 + 3.5417AML | 0.78 |
LAPAM | LAPAM = 32.859 + 3.742AMT | 0.86 | LAPAM = 54.255 + 0.7746AML | 0.68 | |
PAPSM | PAPSM = 8.3944 + 0.1451AMT | 0.86 | PAPSM = 13.942 + 0.0216AML | 0.68 | |
DPSM | DPSM = –26.772 + 4.2591AMT | 0.81 | DPSM = –5.9699 + 0.1653AML | 0.74 | |
DM | DM = 48.778 + 4.9386AMT | 0.80 | DM = 72.092 + 2.5437AML | 0.75 | |
ShW | ShW = 24.212 + 0.5108AMT | 0.81 | ShW = 48.975 + 2.1814AML | 0.67 | |
PAMPNM | PAMPNM = 1.1411 + 0.1053AMT | 0.79 | PAMPNM = 1.7861 + 0.0482AML | 0.59 | |
DNL | DNL = 30.729 + 4.5414AMT | 0.81 | DNL = 56.923 + 0.1445AML | 0.64 | |
A. vexillum | TSL | TSL = 95.015 + 5.3281AMT | 0.80 | TSL = 91.46 + 3.4011AML | 0.69 |
LAPAM | LAPAM = 57.606 + 2.8578AMT | 0.69 | LAPAM = 55.284 + 1.8414AML | 0.61 | |
PAPSM | PAPSM = 30.051 + 0.9754AMT | 0.77 | PAPSM = 33.665 + 0.0576AML | 0.47 | |
DPSM | DPSM = 31.616 + 0.3508AMT | 0.40 | DPSM = 16.745 + 2.66AML | 0.53 | |
DM | DM = 96.02 + 1.6189AMT | 0.40 | DM = 98.573 + 0.8836AML | 0.25 | |
ShW | ShW = 80.021 + 2.7749AMT | 0.47 | ShW = 70.652 + 2.0813AML | 0.56 | |
DNL | DNL = 89.426 + 1.0767AMT | 0.23 | DNL = 87.379 + 0.7421AML | 0.23 | |
P. bicolor | TSL | TSL = 169.58 + 10.566AMT | 0.88 | TSL = 204.44 + 4.7226AML | 0.61 |
LAPAM | LAPAM = 75.166 + 5.314AMT | 0.77 | LAPAM = 86.519 + 2.6928AML | 0.69 | |
PAPSM | PAPSM = 80.544 + 3.5058AMT | 0.59 | PAPSM = 87.839 + 1.7866AML | 0.53 | |
DPSM | DPSM = 30.323 + 0.9515AMT | 0.66 | DPSM = 31.532 + 0.5245AML | 0.70 | |
DM | DM = 160.45 + 9.1931AMT | 0.74 | DM = 177.6 + 4.7868AML | 0.70 | |
ShW | ShW = 62.051 + 3.1587AMT | 0.69 | ShW = 66.768 + 1.7051AML | 0.70 | |
SuW | SuW = 1.6609 + 0.0812AMT | 0.63 | SuW = 1.901 + 0.0377AML | 0.47 | |
PAMPNM | PAMPNM = 3.8235 + 0.1302AMT | 0.65 | PAMPNM = 4.0774 + 0.0672AML | 0.61 | |
DNL | DNL = 97.88 + 4.8372AMT | 0.70 | DNL = 106.2 + 2.5549AML | 0.68 | |
P. atropurpurea | TSL | TSL = 136.44 + 2.654AMT | 0.84 | TSL = 153.29 + 6.7133AML | 0.84 |
LAPAM | LAPAM = –55.099 + 6.4382AMT | 0.78 | LAPAM = 62.818 + 3.4563AML | 0.80 | |
PAPSM | PAPSM = 78.469 + 3.7725AMT | 0.51 | PAPSM = 81.516 + 2.0957AML | 0.56 | |
DPSM | DPSM = 33.683 + 1.355AMT | 0.77 | DPSM = 36.574 + 0.667AML | 0.66 | |
DM | DM = 120.85 + 10.931AMT | 0.68 | DM = 130.25 + 6.0454AML | 0.74 | |
ShW | ShW = 99.603 + 1.8321AMT | 0.64 | ShW = 101.38 + 1.0035AML | 0.68 | |
SuW | SuW = 3.2058 + 0.2142AMT | 0.40 | SuW = 3.5594 + 0.1104AML | 0.38 | |
PAMPNM | PAMPNM = 3.4914 + 0.3815AMT | 0.79 | PAMPNM = 3.9787 + 0.2034AML | 0.79 | |
DNL | DNL = 45.005 + 10.03AMT | 0.78 | DNL = 58.218 + 5.3281AML | 0.78 |
Species of the family Pinnidae are cryptic and can easily adapt to environmental changes (
Five species of the genus Atrina and six species of the genus Pinna representing the family Pinnidae were identified. The number of identified species updates the previous record for this area (
The ecological conditions of the coastal habitats in northern Iloilo apparently define the pen shell species that dominate in an area. For example, many of the six species investigated are different from other areas where pen shells are known to thrive, such as in Sugai Pulai, Malaysia (
The analysis of pen shell morphology relied on nine internal and external characteristics of the valve among species of the genus Pinna and eight characteristics among species of the genus Atrina. The external surface sculpture of the valves and the size and position of the adductor muscles, which create distinctive scars on the inner side of the valves, were used to define individual species of the family Pinnidae, as suggested by
Although no new species were identified in this study, following this comprehensive examination of specimens collected with a more comprehensive survey will lead to the generation of a comprehensive checklist of pen shell species in northern Iloilo. The application of this same method to other known pen shell-occurring areas in the Philippines, such as in the Samar Sea, where an active fishery exists (
The considerable size of the adductor muscle and its nutritional value (
It is important to note that no previous characterization of the adductor muscle was made for pen shells, and the use of this information may give previously unexplored insights about these resources. The linear regression analyses and correlations made with various shell length parameters with adductor muscle thickness and length may enable fishery scientists to determine the impacts of pen shell fisheries on the resources more precisely by closely monitoring the adductor muscles that are sold in the market, but this would even be more realistic if smaller-sized individuals are also represented. With the expected depletion of pen shell resources as harvesting pressure increases, pen shell juveniles may be harvested and secretly sold or brought home for domestic consumption. Perhaps, it is important to include size limitation measures among the strategies to regulate the harvesting of pen shells to ensure the sustainability of this important resource in the area.
Based on the different forms of the marketed adductor muscles, it is evident that species other than A. pectinata, which commands the highest value among all pen shell species, are also accepted for general consumption. The linear regression analyses and correlations between various shell characters and several adductor characters of the six dominant species were done to infer the state of wild pen shell populations. Through this, it is evident that certain characteristics can be used to discriminate the different species under Pinna. The appropriate procedure to do this is to relate the dimensions of the adductor muscles with various characteristics of their shells. Using extracted information from the dominant species, it seems possible to determine the species of their source organisms.
The described and analyzed morphological characteristics of the adductor muscle of A. pectinata, A. inflata, A. vexillum, P. bicolor, and P. atropurpurea suggest that the relations of thickness and length of adductor muscles with the various lengths characters of the shell can be used to differentiate the species by looking at the characteristics of the adductor muscles. The high correlations between various adductor muscle characteristics and shell length characters indicate that they could be a good for taxonomic purposes. The specific and distinct identity of each species in this study has provided information on the diversity of pen shells as well as an opportunity for the newly discovered species to be included in the catalog of bivalves in northern Iloilo, Philippines. Also, through the marketed adductor muscles, it is possible to assess the level of pressure posed by fishers on wild pen shells in this area using established modeling methods. Thus, this study may be useful in stock assessment and in monitoring the sizes of shucked pen shells.
This study is part of the dissertation of the first author, who is a scholar under the Advanced Science and Technology Human Resource Development (ASTHRD) Program of the Department of Science and Technology (DOST). The conduct of her field research was partially supported by “Marine Fisheries Assessment of Panay: Building Local Fisheries Information through Research Capability Enhancement in HEI’s”, a research project that was supported by the Commission on Higher Education (CHED). Permits to conduct the study were granted and additional supporting data were provided by the Municipal Mayors of Carles, Estancia, and Batad, all in Iloilo Province.