Observation of Growth Performance of Coastal Hard Clam Meretrix meretrix in Bottom-based Culture Systems

Abstract

To promote sustainable bivalve aquaculture in estuarine environments, this study evaluated the growth and ecological performance of the Asiatic hard clam (Meretrix meretrix) cultured using two bottom-based systems, fencing and bed-covering, across intertidal and subtidal zones in the Rejukhal estuary, southeastern Bangladesh. Clams were stocked at three densities (150, 200, and 250 individuals/m²) in 1×1 m plots arranged in a randomized block design with triplicates, totaling 27 experimental units. Over five months (February–June), growth, survival, environmental factors, and plankton composition were monitored. Survival rates differed significantly among the evaluated culture systems (p < 0.05). Both the subtidal (62.88 ± 5.80%) and intertidal (64.35 ± 7.14%) fencing systems demonstrated comparable and statistically higher survival compared to the intertidal bed-covering system (55.11 ± 3.10%). Higher survival in fencing systems likely resulted from reduced mechanical stress and sediment accumulation, ensuring better water flow and food availability. In contrast, the bed-covering system experienced net-induced stress and sediment buildup, which likely impaired feeding and lowered survival. Subtidal fencing outperformed others in growth, with shell length increasing from 28.2 ± 1.29 mm to 39.90 ± 1.66 mm. Stocking density and zone had no significant effect on growth or survival, likely due to post-stocking dispersion maintaining effective densities. Growth positively correlated with chlorophyll a (r = 0.72, p < 0.01) and dissolved oxygen (r = 0.65, p < 0.05), and negatively with salinity above 30 ppt (r = –0.54, p < 0.05). The water plankton in Rejukhal coastal waters was predominantly composed of Coscinodiscophyceae and Bacillariophyceae, with peak abundances in April and May. Water plankton abundance showed positive correlations with pH, ammonia, and phosphate, and a negative correlation with turbidity, while temperature and dissolved oxygen had moderate effects. In the gut of cultured M. meretrix, plankton composition shifted over time toward Bacillariophyceae dominance and exhibited stronger positive correlations with dissolved oxygen, temperature, ammonia, phosphate, and pH. Selective feeding analysis indicated that cultured M. meretrix preferentially ingested certain Bacillariophyceae genera such as Amphora and Cymbella, while largely avoiding larger centric diatoms (Coscinodiscophyceae). Benthic macrofaunal diversity, assessed via Shannon Index (H′), Simpson Diversity (1 − D), Species Richness (S), and Evenness, peaked in March (H′ = 1.01) with balanced species composition, declining in later xvii months. A bibliometric review of 1,361 studies (2000–2025) revealed growing interest in sustainable clam aquaculture. Subtidal fencing is recommended as the most effective culture method for M. meretrix. Future work should focus on high-density trials, hatchery seed development, and economic feasibility to enable commercial-scale adoption in South Asia.