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Study on the Diversity and Abundance of Zooplankton in western white shrimp (Litopenaeus vannamei) Farms at the Gomishan Shrimp Site
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Abbasali Aghaei Moghaddam1 *   , Seyyed Morteza Hoseini1 , Melika Ghelichpour1 , Sara Haghparast2 , Abdollah Haghpanah1 , Behruz Garavy1 |
1-Inland Waters Aquatics Resources Research Center-Gorgan, Iranian Fisheries Sciences Research Institute, Agricultural Research Education and Extension Organization (AREEO), Gorgan, Iran , aghaeifishery@gmail.com
2- Department of Fisheries, Faculty of Fisheries and Animal Science, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran |
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Abstract: (29 Views) |
Introduction: Understanding pond structure and performance is essential to enhancing shrimp production efficiency. A critical yet often overlooked factor is the role of natural food sources—such as microalgae, benthos, and zooplankton—in crustacean nutrition (Tacon, 1987; Martinez Cordova et al., 1998). Multiple studies confirm that shrimp, including L. vannamei, prefer live pond organisms over supplemental feed (Hena et al., 2011). Research by Bakhtiari et al. (2012) and Kavyani et al. (2012) identified copepods, rotifers, decapod larvae, and sergestids as dominant planktonic groups in western white shrimp ponds. Shrimp rely on detritus, phyto- and zooplankton, and macrobenthos throughout their life cycle, alongside formulated feed (Farhadian et al., 2014). Moss (2002) demonstrated that up to 53–77% of vannamei growth in non-fed ponds stems from naturally occurring organisms, including plankton and benthos. This study therefore investigates zooplankton diversity and abundance in shrimp ponds and their relationships with physicochemical parameters to optimize natural productivity.
Materials and Methods: Fieldwork was conducted during the Litopenaeus vannamei cultivation cycle (110 days; June to September, 2023) across three 1.2-ha ponds (one per farm: Farms 4, 7, and 10) at the Gomishan Shrimp Farming Site, Golestan Province. Water quality parameters—air and water temperature, pH, dissolved oxygen, oxygen saturation, salinity, TDS, and EC—were measured weekly using a Hach HLC40 portable meter; water transparency was assessed with a Secchi disk. Ammonia and nitrate concentrations were analyzed via Palintest kits. Zooplankton samples (30 L per pond) were collected biweekly from four standardized points using a 60-μm mesh net and fixed in 4% formalin (1 L containers). In the lab, subsamples were identified and counted under a microscope following Tomas (1997) and Barnes (1978). Pearson’s correlation assessed links between zooplankton abundance and physicochemical variables. Biodiversity indices (Simpson, Shannon-Wiener, Pielou’s Evenness, Margalef) were calculated using PAST 3; all statistical analyses were performed in IBM SPSS v22.0.
Results and Discussion: In this study, the zooplankton assemblage comprised foraminiferans, copepods, copepod nauplii, various free-living nematodes, larvae and juvenile worms of Streblospio gynobranchiata, gammarids, insect larvae of Ephydra sp., and occasionally rotifers. Copepods were overwhelmingly dominant across all farms and sampling dates, reaching a peak abundance of 151.05 individuals per liter in mid-July, representing the highest density recorded throughout the entire cultivation period. No statistically significant differences were observed among farms at any sampling time for physicochemical parameters including temperature, pH, dissolved oxygen, salinity, TDS, and water transparency. However, salinity and TDS showed a consistent upward trend from the late June to early September, likely due to evaporation and limited water exchange. No significant inter-farm differences were detected in ammonia or nitrate concentrations at corresponding time points; yet, nitrate levels increased significantly by the end of the culture cycle compared to initial values, while ammonia concentrations remained relatively stable—indicating active nitrification within the ponds. Biodiversity indices revealed pronounced temporal changes: Simpson’s Index: Increased from 0.41 (early cycle) to 0.91 (late cycle), reflecting strong dominance by a few taxa (mainly copepods). Shannon-Wiener Index: Declined sharply from 1.00 (early) to 0.14 (late), indicating severe loss of species richness. Pielou’s Evenness Index: Ranged between 0.63 and 0.94, showing moderate decline toward season end. Margalef’s Richness Index: Decreased from 0.76 (early) to 0.17 (late), confirming substantial reduction in species diversity over time.These results indicate that although total zooplankton abundance remained high due to copepod dominance, species richness and community evenness declined markedly during the cultivation cycle, suggesting progressive homogenization and ecological simplification of the pond ecosystem.Correlation analysis between total zooplankton abundance and environmental variables revealed a moderate negative correlation with salinity (r = –0.474), but no significant correlations with temperature, pH, dissolved oxygen, TDS, EC, ammonia, or nitrate. A moderate negative correlation was also found between salinity and dissolved oxygen (r = –0.438), and a weak positive correlation between salinity and pH (r = 0.302). The findings confirm that Litopenaeus vannamei relies substantially on natural food sources including zooplankton, detritus, phytoplankton, and benthos to meet its nutritional requirements, contributing to the low FCR values (0.52–0.77) observed in this study. Farhadian et al. (2014) reported similar patterns, emphasizing that shrimp utilize live food resources throughout their life stages, with consumption rates dependent on age and availability. Bakhtiari et al. (2012) identified copepods, rotifers, decapod larvae, sergestids, and crustacean larvae as the dominant components of zooplankton communities in Dalvar shrimp ponds. Kavyani et al. (2012), studying western white shrimp farms in Bushehr, found rotifers to be the most abundant group among 13 identified animal plankton genera.
Conclusion: According to the results of this study, copepods constituted the majority of the zooplankton community, while the low density of rotifers and the absence of cladocera could be due to high salinity. Biological indices showed that the farms were poor in terms of species richness. This is probably due to the use of fine filters and unfavorable conditions at the end of the culture season such as increased salinity, organic matter and decreased temperature. |
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| Keywords: Gomishan shrimp site, physical and chemical characteristics, Litopenaeus vannamei |
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Type of Study: Research |
Subject:
Special
Received: 2025/07/7 | Accepted: 2025/09/3
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