3. Pond-Based AIA
Fish culture in ponds has long been practiced by rural communities in many or several countries in Asia and is a current practice in Africa. Pond culture is an extremely known aquaculture production strategy. It can be divided into two sorts depending on their water supply, namely levee ponds (1.79 m
3/kg productivity) and watershed (or depression) ponds
[25][23]. Pond sizes fluctuate from 100 to 100,000 m
2, depending on their production scale, site, and species types. Ponds have a typical depth of 1.2–1.5 m
[25][23]. Most fish farming families in rural communities are engaged in extensive and semi-intensive farming because of the absence of resources
[26][24], so fish productivity is variable
[27,28,29,30,31][25][26][27][28][29]. AIA systems typically range from extensive to intensive types of aquacultures, and they frequently rely on fertilization of some kind to produce phytoplankton and zooplankton as natural fish food
[32][30] (Edwards et al., 2000). According to the type of structure utilized in operation, such as cage, pond, or tank farming systems, aquaculture can be further classified.
The first (1st) most applicable scenario is the entry of pond-dike (dam) crops in rural Bangladesh, Malawi
[36][31], bamboo fish in China, and Egypt as El-Riad-Tourism-Lake
[37][32], where the mud of the pond rich with nutrients is utilized to compost.
Vegetables and fruit trees allow some fruits to grow on pond dams, for example, bananas, lemon, coconut, guava, palm, orange, bamboo, and papaya. Pond slopes are also utilized for growing vegetables (e.g., beans, squash, and cucumber) using bamboo structures to aid their spread over the pond water
[38][33]. Notwithstanding, a few aquatic weeds are applied as fodder (grain) for fish and livestock, such as “Azolla, duckweed, water hyacinth, and water spinach”
[26,39][24][34].
3.1. Impact of Pond-Based AIA on Soil, Fish, and Plant Characteristics
Fish pond wastewater is sometimes utilized as a potential irrigation resource to grow vegetables around places that are directly or indirectly used by humans
[41][35]. The presence of organic feeding waste, nitrogen, and phosphorus in the lower part of the pond contrasted with the surface water could directly influence water quality, increment parasite infection, nutrient accessibility, fish growth, and production due to the exchange of substances among soil and water
[42,43][36][37]. Total alkalinity and ammonia nitrogen (TN) are higher at the soil–water interface when contrasted with the surface water
[44][38]. The accumulation of nutrients in the sediment increases directly with total nutrient input in a limited-scale freshwater pond
[45][39]. Recycling water in an AIA is not only an approach to saving water, but it can also be a source of fertilizer (organic) to soils with lower fertility to give a higher efficiency of crops. The efficiency of nutrient water aquaculture (17–340 g of protein/m
3 water) is the most noteworthy among all significant food-producing sectors, including the production of animals and vegetables
[46][40]. Fish wastewater irrigation was good for enhancing soil physical and chemical properties, the nutrient perquisites of the soil, growth parameters, and productivity of crops such as maize, okra, and cucumbers
[47,48,49][41][42][43].
3.2. Water Use Efficiency (WUE)
The range of average WUE is reported to be 0.56–1.59 and 0.94–1.10 kg/m
3 for maize, and wheat, respectively. For aquaculture, WUE accounts for 0.21–0.37, 0.71–2, and 0.02 kg/m
3 in well-managed ponds, super-intensive recirculating, and extensive systems, respectively
[57][44]. The WUE in pond-based AIA systems is 2.13 kg/m
3 for fish–maize production and up to 8.46 kg/m
3 for fish–vegetable production
[4]. The upshot is that the WUE in pond-based AIA is more than in the non-AIA system. Therefore, using fish pond effluent to irrigate crops in integrated systems is preferable.
3.3. Economics, Social, and Environmental Benefits of Pond-Based AIA
Reusing wastewater from fish farming for irrigation reduces fertilizer costs
[59][45]. The gross revenue from tilapia production (on 1 ha of land) for two production cycles in a year is US$ 960 × 20 with net revenue of US$ 384 × 20, while the gross margin is about US$ 466 × 20 per year
[60][46]. The rate of return on investment represented by percent profit is 66.7%, which is equivalent to a 1.67 production efficiency index that shows how beneficial tilapia cultivation is, despite tilapia farmers exceeding cost by 67%
[60][46]. In Malawi
[38][33], AIAS was 11% more fertile than non-AIAS, and the incomes of AIAS farmers increased by 134%/ha. The median annual income of farmers in AIAS and non-AIAS was $185 and $115, respectively. Therefore, fish farming directly contributed to an increase in productivity, profitability, and income for the AIA farm.
In Kilombero
[7], AIA-based farming systems, including fish and vegetables (
B. Rapa Chinensis), resulted in a three and 2.5-fold increase in net production compared to fish and vegetable farming alone in non-integrated systems, respectively. In selected areas of Bangladesh
[61][47], it has been observed that a large number of agricultural enterprises (crop, poultry, fisheries, cattle, etc.) and a large area of land ponds increase the income of farmers
[62][48]. Finally, pond-based AIA produced fish, crops, and protein and increased farm productivity and farm net income per hectare (ha) by 11% and 134%, respectively, compared to pond-fish culture or non-AIA
[7,37,62][7][32][48].
Pond-based-AIA is considered an ecologically sustainable system as it provides water/nutrients recycling ability and increases both productivity and water usage efficiency
[8]. Fish waste improves soil fertility by increasing the number of organic fertilizers and renewing nitrogen and phosphorous elements. The fertilizer is dredged from the bottom (lower part) of the ponds to be used as a successful fertilizer to enhance crop production
[12]. Furthermore, vegetables and herbs were grown on the pond sediments to protect the embankments (dikes or levees) from erosion by rain.
4. AIAS in Coastal Areas
In recent decades, saltwater shrimp cultivation has increased significantly in Asia’s inner and coastal areas, including river deltas, with well-known environmental effects on mangroves and other biotas
[94,95][49][50]. Additionally, agriculture has significant repercussions, particularly in Thailand, Bangladesh, and Vietnam
[95,96][50][51]. In the inland areas of Thailand, where rice is grown extensively with irrigation that traditionally relies on free water, interference between agriculture and aquaculture is notable
[96,97,98][51][52][53]. During the dry season, saltwater naturally enters these areas, and during the wet season, it can be retained in ponds and mixed with fresh water to provide saltwater shrimp with ideal conditions for growth. In the 1990s, the seepage and release of water from ponds caused severe pollution of irrigation water and agricultural soils
[95,99][50][54]. In 1998, the Thai government responded by prohibiting shrimp aquaculture in some areas
[95][50]. However, enforcement has not always been consistent. Shrimp are favored by economic incentives to such an extent that hypersaline water and even bagged salt are trucked in to maintain shrimp growth conditions, despite the adverse effects on nearby agriculture
[95,100][50][55].
In Bangladesh, shrimp aquaculture relies on trapped seawater carried inland by tides through constructed and natural channels. The ponds allow water to escape through percolation and overflow, accumulating sediment from upstream runoff. During the growth season, water is also frequently released, and then after each annual cycle of shrimp culture, the contents of ponds are pumped onto adjacent land
[95][50]. Soils can become unsuitable for agriculture as a result of sedimentation and the release of saltwater from ponds in this manner
[95][50].
In the UAE
[69][56], the desalinated water is used to irrigate a wide variety of high-value crops such as radish, cauliflower, maize, lettuce, spinach, amaranthus, carrot, tomato, mustard, asparagus, eggplant, and quinoa. On the other hand, about 150 m
3/day of brine water is utilized for aquaculture, which is followed by irrigation salinity-tolerant forage grasses and halophytes. The outcomes obtained within four months demonstrated that the weight of fish increased by 200% and the length of fish increased by 60%. Two species of fish,
Sparidentex hasta (sobaity seabream) and
Oreochromis spilurus (tilapia), demonstrated remarkable adaptability to the local conditions.
In Brazil
[80][57], diluted brackish aquaculture effluent is used to irrigate
Enterolobium contortisiliqum seedlings. The outcomes revealed increased shoot growth and the total dry weight in
E. contortisiliquum. These outcomes indicate that saline aquaculture effluent can be reutilized to irrigate tree species.
In Egypt, some projects were completed in a salty environment, such as El-Gouna Park (water salinity 15 g/L)
[37][32] rula for land reclamation (RLR)
[37][32]. In the RLR project, groundwater with a salinity of more than 26 g/L was utilized for European seabass (
Dicentrarchus labrax) and gilthead seabream (
Sparus aurata) cultivations. After that, water was used for
Sarcocornia planting. RLR is not operational due to the high cost of electricity, which in the end represented more than 30% of the total production cost and made further use unprofitable.
Salinity is an emerging issue that results in significant yield losses in many parts of the world, particularly in arid and semiarid regions. Soil acidification, groundwater pollution, land subsidence, and other hydrological perturbations can shift away from agriculture
[95,101][50][58]. However, it is challenging to mitigate soil salinization. Consequently, the long-term economic benefits of fish and shrimp culturing may not be realized. As a result, economic stimuli and localized environmental factors significantly influence the integration that makes up the precarious balance between aquaculture and agriculture
[95,102][50][59]. Farmers frequently face a difficult choice: They can continue fish and shrimp cultivations, mitigate cropland salinization, or maintain agriculture.