Reproductive pattern and gut content analysis of asiatic hard clam meretrix meretrix (linnaeus, 1758) in Marudu Bay, Malaysia
Asiatic hard clam, Meretrix meretrix is the indigenous bivalve species found in Sabah coastal areas and is an important species for artisanal fisheries, especially in Marudu Bay, Sabah. The present study was carried out to understand some aspects of reproductive biology such as sex ratio, stages of...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2023
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/40763/1/24%20PAGES.pdf https://eprints.ums.edu.my/id/eprint/40763/2/FULLTEXT.pdf |
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| Summary: | Asiatic hard clam, Meretrix meretrix is the indigenous bivalve species found in Sabah coastal areas and is an important species for artisanal fisheries, especially in Marudu Bay, Sabah. The present study was carried out to understand some aspects of reproductive biology such as sex ratio, stages of gametogenesis, temporal variation in the condition and gonad index of the clam, and its relationship to the environmental parameters of its habitat. This study was also conducted to determine the main diet of the clam and the composition of food particles in the clam’s gut in comparison to the food particles found in their habitat and the environmental parameters that could affect and influence the clam’s feeding selection. Sampling was carried out once a month for 10 months (May 2019 to February 2020) in Marudu Bay. Clam samples, environmental parameters, and water samples (for seston, chlorophyll-α, water quality and nutrients analyses, phytoplankton, and zooplankton) were collected at the sampling areas during the study period. Clam samples were collected using clam fishing gear called the ‘kerek’ from the substrate during low tide. A total of 750 clam samples were used for condition index, histological, and gut content analyses. Results showed that the clam is dioecious and its population in the bay was slightly skewed toward female clams (1.058:1) with the occurrence of hermaphrodite at an extremely low frequency (0.4%). The clam was noted to spawn throughout the year with two spawning peaks (June to July and November to December). There was a significant difference (p<0.05) in the condition index between the months. However, there was no significant difference (p>0.05) observed in the gonad index between the months and between the male and female gonad index. The condition index of the clam in the bay fell into the moderate fatness category and showed correlations with various environmental variables while the gonad index only showed a correlation with total rainfall. As for the gut content analysis, a total of 1475 food particles were found in the gut of the clams. Phytoplankton and zooplankton represented about 80.9% and 19.1% of the total food particles found in the gut of the clam, respectively. Meanwhile, diatoms were the most common food particles ingested by the clams with 95.81% and dinoflagellates only contributed about 4.19% of the total phytoplankton ingested by the clams. The five most dominant phytoplankton genera found in the gut of the clam throughout the study period are Nitzschia (24.71%), Coscinodiscus (23.38%), Cyclotella (13.70%), Pleurosigma (12.68%) and Navicula (8.95%). The dendrogram of similarity showed that the phytoplankton compositions of the water sample and in the gut were grouped apart. The result of One-way ANOSIM analysis comparing phytoplankton composition in gut and water samples indicated significant differences for all the months with an overall average R: 0.717, p<0.001. In general, the similarity between phytoplankton in the water sample and the gut was less than 50% and two clusters can be depicted. Cluster 1 had a similarity of less than 40% and Cluster 2 had a similarity between 40-50%. Cluster 1 (September 2019) showed significant differences between phytoplankton in the water sample and in the gut with R: 0.924, p<0.008. Meanwhile, all months except September 2019 were grouped in Cluster 2 with R: 0.788, p<0.008. The result from PERMANOVA following distance based linear modeling (DistLM) demonstrated that phytoplankton cell density, phytoplankton diversity, chlorophyll-α, and salinity were significantly (p<0.05) influencing the selective feeding behavior of the clam. The clam population in Marudu Bay is balanced with a reproductive pattern that is active all year round and has short resting and spent stages like most tropical bivalves due to the high annual temperature and constant food supply throughout the year. The clam showed obvious selective feeding behavior where more benthic diatoms were selected as food due to the nutritional content, quantity, and availability of benthic diatoms in the clam's natural habitat. Although various environmental parameters influence the clam in various aspects, it was discovered that salinity is an important parameter influencing not only the condition index and gonad index but also the clam's selective feeding behavior. Drastic changes in salinity affect the condition and trigger the spawning of the clam. Meanwhile, at certain salinities, the feeding physiology of the clam, such as filtration and ingestion rate, reaches an optimum range and the clams actively filter food from the water column, making their selective feeding behavior more efficient. |
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