Based on the study conducted by the BPD in 2021, it was found that the Manakku Village has a pond area of 453.00 hectares, which constitutes 17.32% of the total pond area in the Labakkang District and 4.44% of the Pangkep Regency's overall area. The farmers in Manakku Village predominantly use three types of cultivation systems: (1) fish monoculture, (2) shrimp monoculture, and (3) fish and shrimp polyculture. For the purpose of this research, the milkfish monoculture cultivation system will be employed. Furthermore, three levels of technology packages have been implemented in the village, namely (1) traditional plus cultivation system, which covers approximately 75% of the farms, (2) semi-intensive cultivation system, which covers around 20%, and (3) intensive cultivation system, which covers only about 5% of the farms. It's worth noting that the intensive cultivation system's application in the village is relatively short-lived.
Intensive cultivation systems, which rely heavily on agricultural technologies, can often lead to short-term gains but are not sustainable in the long run. These systems often force nature to produce beyond its carrying capacity, leading to environmental degradation and depletion. Such practices can result in barren and rugged lands that take a long time to recover. To ensure sustainable agriculture, it is essential to adopt ecologically and climate-based practices that work in harmony with nature. The location of the pond land in Manakku Village is promising, as it is surrounded by water sources, including the coastal waters of the Makassar Strait and three rivers, namely the Lompoa River to the North, the Cakarri River to the East, and the Bontoala River to the South. However, recent field interviews have revealed that it is challenging to find mustard greens or pond workers in the area. This is likely because the pond products are not profitable enough to meet household living needs, and many are seeking alternative jobs that offer better economic opportunities. Therefore, it is crucial to develop sustainable agricultural practices that are economically viable and promote environmental conservation (BPD, 2021).
One of the challenges faced by pond farmers is the low survival rate of milkfish, which can sometimes be as low as 50%. Previous research studies (Budiasti et al., 2015; Barman et al., 2012) have reported slow growth rates and suspected that in addition to seed quality, pond quality may be a contributing factor, particularly in cases where ponds have reached saturation levels (Aris et al., 2021). To address this issue, farmers have explored the use of modular cultivation systems or relocation, as aquatic organisms tend to thrive in new environments. These findings highlight the importance of considering both seed quality and pond management strategies to improve milkfish survival and growth rates in pond farming (Lin, 1985; Lawson, 1995; Lekang, 2007; Barman et al., 2012).
The elevation of Manakku Village from the sea level is between 0-1.5 meters. As a result, the rice fields that are susceptible to saltwater intrusion may be converted into pond land, which can have significant impacts on the ecology of the area. Moreover, the tidal conditions are highly variable, ranging between 0-1.5 meters. However, scientific research has shown that the average tide height is between 0.8–1.2 meters. During certain months, such as December and May, high tides reaching 1.5 meters occur only during a full moon. This phenomenon has led to the opening of new fishponds, which are vulnerable to intrusion by foreign water during high tides. This inconsistency in saltwater seepage poses a significant challenge for rice field maintenance. Consequently, many rice fields are being converted into fish ponds. However, this conversion is also not without its challenges, as regular saltwater intrusion is necessary for the fish ponds to function effectively. As a solution, many new ponds are being constructed with drilled wells to ensure regular saltwater seepage, thereby allowing for the effective conversion of rice fields into fish ponds.
The Manakku Village has annual ups and downs in tidal patterns require farmers to adapt their fish and shrimp stocking schedules to reduce mortality rates. The fluctuations in salt levels during these tidal transitions are closely related to the osmoregulation process of fish and shrimp. High salt levels are necessary during their young age, while low salt levels are required in old age. Therefore, the farmers must monitor the salt levels closely and adjust their farming practices accordingly to ensure optimal growth and survival rates (Lekang, 2007).
Aquatic organism cultivation in a pond is heavily reliant on the condition and construction of the pond itself. According to studies conducted by Lin (1985), Lawson (1995), and Lekang (2007), a pond unit comprises of bunds, channels, and doors. The dike, which functions as a water-holding structure, must be solid and free from leaks. The channel connecting the water source and the pond must be of an appropriate width to match the outside perimeter of the pond and be free from grass, rubbish, and sediment to withstand currents. Moreover, the pond unit must include systems to regulate the volume of water in the pond. These factors are critical to the success or failure of aquatic organism cultivation and must be considered when constructing and maintaining a pond (Tsai et al., 1970; Lawson, 1995; Garg & Bhatnagar, 2003; Bhatnagar, 2010)
The construction of a pond involves various interconnected systems, including the pond bottom, the bottom of the door, and the channels (Buschman et al., 2004; Rangka & Asaad, 2010). In order to achieve the desired cultivation goals, it is essential that the pond bottom is higher than the bottom of the gate, the bottom of the gate is higher than the bottom of the channel, and the bottom of the channel is higher than the lowest tide in coastal waters. This ensures that water management can be achieved through gravity, without the need for a pumping system. Proper design of the pond and its components is crucial for the maintenance of a healthy aquatic ecosystem and the sustainability of the cultivation practices (Tsai et al., 1970; Lawson, 1995; Garg & Bhatnagar, 2003; Bhatnagar, 2010)
According to the findings of our observations, it has been noted that the construction of ponds in Manakku Village often fails to comply with the recommended technical guidelines for constructing ponds. The following observations can be made in a sequential order: (1) The pond bottoms are often shallow, which limits their capacity to accommodate large volumes of water. This can potentially lead to water scarcity and affect the aquatic ecosystem within the pond; (2) The bunds, or embankments, are often found to be low and prone to leaks and seepage. As a result, maintaining the desired water level in the pond becomes a challenge, which can have a significant impact on the aquatic habitat's health and diversity; (3) The main and hatch doors of the ponds are generally narrow, which can limit their ability to regulate the water volume effectively. This can result in the accumulation of water in some areas and water scarcity in others, which can lead to imbalances in the aquatic ecosystem; (4) The narrow channels leading to the ponds often contain grass, rubbish, and sediment, which can impede the flow of water in and out of the pond unit. This can lead to water stagnation, which can adversely affect the health and diversity of aquatic life within the pond. It is essential to adhere to the recommended technical guidelines for pond construction to ensure the proper functioning of aquatic ecosystems within the pond.
The seven pond preparation steps must be carried out thoroughly because they are interrelated to achieve the goal of cultivating aquatic organisms (Lawson et al., 1995; Garg and Bhatnagar 2003; Bhatnagar,2010; Lekang,2007). Previous research has shown that the low survival rate and slow growth rate of milkfish in ponds is a major challenge faced by pond farmers (Bhatnagar, 2003; Bhatnagar, 2010; Lekang, 2007). According to Bhatnagar (2003), poor quality seeds and the condition of ponds that have already reached saturation are among the factors causing low fish survival and slow growth rates. To overcome the issue of saturated pond soil, proper preparation and provision of nutrition to ponds are required, such as the provision of manure. However, in general, pond farmers do not consider pond preparation to be very essential. Therefore, it is necessary to raise awareness among farmers about the importance of pond preparation and the provision of proper nutrition to improve the survival rate and growth rate of milkfish (Tsai et al.,1970; Lawson, 1995; Garg & Bhatnagar, 2003; Liao et al., 2004; Bhatnagar,2010).
The issue of pond land saturation can be addressed through the use of a modular cultivation system, which involves the movement of the cultivation system from one plot to another within a single maintenance cycle (Jamerlan et al., 2014; Hanke et al., 2020). This system allows for the occupation of multiple plots by the cultivated organisms during one rearing cycle. In the present study, milkfish will be used as the cultivated organisms and will occupy three plots. Plot A will serve as the nursery plot and will function as a seed reservoir for a year, providing acclimatization and seed production capabilities. Plot B will serve as the first stage of the enlargement plot, with a maintenance period of approximately two months. Lastly, plot C will serve as the second stage of the enlargement plot, with a maintenance period of approximately two months.
The present study was conducted over a period of one year, and involved three stages or maintenance cycles. Each maintenance cycle lasted for a duration of four months, during which two rearing plots were utilized for the cultivation of organisms. The two grow-out plots, namely plot B and plot C, were provided with the same opportunity of two months each for the pond preparation period as previously described - from drying to growing natural food. The modular cultivation system employed in this study offers a potential solution to improve the survival and growth rate of milkfish (Santander et al., 2015; Saraswaty et al., 2017; Rinaldi et al., 2019). The construction of modular cultivation system ponds.
The results indicate that the overall average of the measured parameters is still within the optimal range for plant growth. However, the salt content in the water during August, September, October, and November was found to be above the optimal range for milkfish cultivation. Despite this, the milkfish were able to survive during these months, but could only be harvested during the third cycle in August and September. In contrast, during the start of the first cycle in October and November, and as we enter December and January, the growth of milkfish accelerates faster. According to experts in the field (Villalus & Ungguni, 1983; Swan, 1997; Burt et al., 2011; Banman et al., 2012; Cheng et al., 2018; Aris et al., 2021), all aquatic organisms require salt levels for their maturity, including milkfish. It is essential to note that fluctuations in the salt levels of the water during the year can have a significant impact on aquatic life.
The present study revealed that tidal fluctuations significantly impact several water quality parameters such as oxygen, temperature, and salinity. The salinity parameter is particularly affected due to the temperature fluctuations. The research conducted by Kale (2016), Amsari et al. (2017), Guanzon et al. (2004), Muanif et al. (2019), Astuti & Warsa (2020) indicates that there is a direct linear correlation between temperature and salinity. An increase in water temperature by 1–2 degrees Celsius leads to an increase in salinity by 1–2 ppt. These findings have been supported by various other researchers as well (Jania, 2006; Portner, 2009; Aris et al., 2021).
The present study’s finding suggest that a longer nursery period, which involves stunting or restraining the growth rate of the fish seeds, can lead to higher survival rates. This is consistent with prior research in the field and highlights the importance of carefully managing the growth and development of milkfish in aquaculture settings (Tsai et al., 1970; Malle et al., 2019; Fauziah, 2019; Amsari et al., 2019; Borlongan et al., 2003; Mwangamilo & Jiddaw, 2003; Pramata. Et al., 2017; Ofori et al., 2018).
The first cycle recorded a low survival rate of 91%, which can be attributed to the high temperature of 32°C. Previous studies have shown that aquatic organisms, including milkfish, have a range of optimal temperatures that support their survival rate (Ismail et al., 1993; Santander et al., 2015; Ramadhani et al., 2021; Adul et al., 2022). The literature suggests that the high survival rate for milkfish (Chanos chanos) is within the range of 27–31°C, which is consistent with the results obtained by several researchers (Tsai et al., 1970; Lawson, 1995; Garg & Bhatnagar, 2003; Liao et.al, 2004; Bhatnagar, 2010).
The results suggest that salinity has a slightly lower impact on survival rates compared to temperature, owing to the relative stability of salinity as compared to temperature fluctuations. It is noteworthy that a survival rate of 91% was achieved at a salinity of 42 ppt, which can be attributed to the euryhaline nature of milkfish, as it is capable of surviving in a range of salinities from 0–50 ppt (Mmochi & Mwandya, 2003; Chang et al., 2019; Beeltram et al., 2020; Barman et al., 2021), although milkfish require an optimal salinity range of 10–25 ppt (Adul et al., 2022).
During the second cycle, the survival rate of milkfish showed a significant improvement, reaching 95%. However, this rate is still lower than that observed during the third cycle, which was 97%. The increase in the survival rate during the second cycle can be attributed to a decrease of 1 degree Celsius in the highest temperature, which fell within the tolerable range of 27–31°C for milkfish survival, as reported in previous studies (Adul et al., 2022; Ismail et al., 1993). Similar findings were reported by Salam and Darmawati (2017), thereby providing additional support to the notion that milkfish survival is optimal within this temperature range (Kumagai, 1990; Jaikumar et al., 2013).
Approximately 89% of the variation in survival rate can be explained by the variation in salinity. However, it is essential to note that the impact of salinity on survival rate is relatively lower compared to temperature. This is primarily because temperature fluctuates more significantly than salinity. The survival rate of milkfish is significantly affected by temperature, especially during sudden temperature changes. On the other hand, salinity is relatively stable and less variable than temperature. Based on the data presented in the figure, it can be observed that a survival rate of 95% is achieved at a salinity range of 42–45 ppt. This is possible because milkfish is one of the euryhaline aquatic organisms that can tolerate a wide range of salinity, from 0 to 50 ppt. However, it is important to note that milkfish prefers an optimal salinity range of 10–25 ppt. In summary, the correlation between salinity and survival rate of milkfish is significant, but its impact is relatively lower than temperature. The optimal salinity range for milkfish culture is between 10–25 ppt, although the species can tolerate a wider range of salinity (Tsai et al., 1970; Lawson, 1995; Garg & Bhatnagar, 2003; Liao et al., 2004; Bhatnagar, 2010).
The third cycle exhibited a noteworthy increase in the survival rate of milkfish, which escalated to 97%. This improvement was attributed to the fact that the highest temperature in the third cycle was lowered by 1 degree to 31oC, which falls within the range of temperature that milkfish can endure, as evidenced by previous research (Tsai et al., 1970; Lawson, 1995; Garg & Bhatnagar, 2003; Liao et al., 2004; Bhatnagar, 2010). The aforementioned research highlights the high survival rates of milkfish (Chanos chanos) within the range of 27-31oC degrees Celsius. Similar results were also obtained in the research findings of Salam and Darmawati (2017).
Approximately 99% of the variation in survival rate can be attributed to variation in salinity. It is important to note that the influence of salinity on survival rates is lower than that of temperature, as temperature is more prone to fluctuation while salinity remains relatively stable. Nonetheless, based on the data presented in the above figure, it can be seen that a survival rate of 95% is achieved at a salinity of 42–45 ppt. This is possible because milkfish are euryhaline, meaning they are capable of living in a wide range of salinity levels, from 0–50 ppt (Borlongan, 1992; Borlongan & Caloso, 1993; Borlongan & Caloso, 1994; Barman et al., 2021). However, it is worth noting that milkfish require an optimal salinity range of 10–25 ppt for optimal survival and growth (Requintiana et al., .2006; Wu Lie, 2012; Davidson et al., 2014; Adul et al., 2022).