The primary objective of this trial was to study the effects of stress caused by stocking density in tilapia (Oreochromis niloticus) cultured in the in-pond raceway system (IPRS). Fingerlings (Initial body weight = 30.00 ± 1.20 g) were reared at different stocking densities i.e. low stocking density (n = 13,000; 1.77 kg/m3), medium stocking density (MSD) (n = 17,000; 2.32 kg/m3), and high stocking density (HSD) (n = 21,000; 2.86 kg/m3), all confined within the raceways of the IPRS. Each group was studied in triplicates. The observed growth revealed a regression in the HSD treatment, evident in its reduced weight gain per fish per day, in contrast to other treatments. Survival rate across all treatments was above 99%. Notably, the HSD treatment exhibited an elevated level of cortisol; however, this intensified crowding stress did not significantly undermine the nutritional value of the fish in HSD and other experimental treatments. Furthermore, an elevation in the levels of superoxide dismutase, catalase, and glutathione peroxidase was noted within the HSD treatment in comparison to the other treatments to reduce the damage caused by reactive oxygen species. As the trial proceeded, functions of digestive enzymes like amylase, protease, and lipase diminished consistently across all treatments. This could possibly signify a deliberate redirection of energy resources toward stress alleviation rather than the usual digestive processes. In summation, it can be reasonably deduced that a stocking density of approximately 2.32 kg/m3 (MSD) emerges as the optimal threshold for effectively cultivating tilapia within an intensive aquaculture framework.

This study scrutinized the nutritional quality and serum biochemical indices of grass carp (Ctenopharyngodon idellus) cultivated in traditional pond intercropping (TPI) and in-pond raceway system (IPRS) aquaculture setups. The findings showed that the TPI group exhibited a superior water-holding capacity, while the IPRS showcased heightened crude lipid content and levels of textural properties such as springiness. Moreover, significant differences emerged in the fatty acid profiles, with the TPI group manifesting higher total polyunsaturated fatty acids (ΣPUFAs), EPA, DHA, and Σn-3, while the IPRS group exhibited elevated total saturated fatty acids (ΣSFAs). In terms of amino acids, valine and histidine levels were notably higher in the IPRS group, whereas lysine levels were reduced. Volatile compound analysis revealed significant variations, with the IPRS group containing more volatile substances with a better aroma, resulting in a better odor. The IPRS group performed better in serum biochemistry analysis. Additionally, grass carp in the IPRS group displayed an improved structure and greater coverage area of the visceral peritoneum, appearing lighter in color compared to the TPI group. TPI mainly influences nutritional elements; IPRSs primarily affect muscle texture, serum biochemistry, and overall health. This study aims to fill the gap in quality comparison research and provide an important scientific basis.

Genetically improved farmed tilapia (GIFT, Oreochromis niloticus) are intensively farmed in China, where most of the yield derives from the pond culture system (PCS). The in-pond raceway system (IPRS) is a new type of highly efficient aquaculture mode, and has been recommended as a novel system for GIFT farming. To determine the effects of these culture modes on the gut microbiome of GIFT, we conducted a 90-days experiment in IPRS and PCS units. A 16S rRNA gene profile analysis showed that the composition of gut microbiota in GIFT under IPRS and PCS conditions gradually separated as rearing progressed, with divergent responses by the midgut and hindgut bacteria. The α-diversity in hindgut decreased significantly by day 90, as compared with on day 7 (p < 0.05), with a significantly greater decrease in PCS-reared fish than in IPRS fish (p < 0.05). The α-diversity of microbiota in midgut remained stable (p > 0.05). The overall dominant gut bacteria were Bacteroidetes, Proteobacteria, and Firmicutes. Rearing mode affected the taxonomic profile of the gut bacteria; in midgut, IPRS samples had more Firmicutes and Fusobacteria compared with PCS samples, but less Proteobacteria, Verrucomicrobia, and Actinobacteria. Firmicutes was enriched in IPRS hindgut, and Fusobacteria was enriched in PCS hindgut. Using random-forest models and LEfSe, we also screened core taxa that could discriminate between the gut microbial communities under IPRS and PCS conditions. The genus Cetobacterium (of family Fusobacteriaceae) was significantly enriched in midgut in IPRS fish, and enriched in hindgut in PCS fish. The genus Clostridium sensu stricto (of family Clostridiaceae 1) was significantly enriched in both IPRS midgut and hindgut. Analysis with PICRUSt2 software revealed that the culture modes were similar in their effects on the gut microbial metabolic functions. The predicted pathways were significantly enriched in the metabolism class (level 1). Further, the relative abundance of functions related to amino acid metabolic, carbohydrate metabolic, energy metabolic, and metabolic of cofactors and vitamins were high at hierarchy level 2, as the metabolic activity of intestinal bacteria is especially active. Overall, this study enhances our understanding of the characteristics of gut microbiota in GIFT under IPRS and PCS culture modes. Moreover, our findings provide insights into the microecological balance in IPRS units, and a theoretical reference for further development of this culture system.

Due to its ability to collect and remove aquaculture waste, an in-pond raceway system (IPRS) has been used to decrease the uncontrolled waste discharge in the traditional cage aquaculture method in large water bodies. However, when applied to large water bodies, its environmental performance is still lacking. This study focused on analyzing the microbial characteristics and the interaction between largemouth bass (gill and gut) microbiota and the environment (water and sediment) microbiota of an IPRS. Further, it revealed the primary relationship from the perspective of microbiota in the IPRS. The results show that (1) the alpha diversity of microbiota in the water is significantly lower than that of fish and sediment. The relationship between water microbiota and fish microbiota is limited. (2) The water microbiota inside and outside the tank showed high similarity and were not significantly affected by environmental factors. (3) The SourceTrack analysis showed that fish microbiota is one of the primary sources of sediment microbiota, and more than 15% of the sediment microbiota come from fish. Microbes such as Faecalibacterium, Escherichia-Shigella, and Bacteroides can significantly enrich the sediment. Our study revealed the characteristics and preliminary interaction of fish and environmental microbiota in the IPRS. It provided a reference for evaluating microbial health status in the application of IPRS in large water bodies\' aquaculture.

In-pond raceway system technology (IPRS) was introduced in Pakistan in 2019 as solution for sustainable aquaculture approach by effectively increasing production, reducing pollution and facilitating feed and pond management. Fingerlings of GIFT Tilapia (Oreochromis niloticus) (n = 16,500 in each raceway, initial weight = 32.00 ± 1.26 g) were stocked in June 2019 in two IPRS raceways (area of each raceway = 220 m3) for 171 days until harvested on November 30, 2019. Fingerlings stocked in traditional earthen ponds (area of each pond = 6167 m3) were studied as control (n = 3000 in each pond, initial weight = 32.00 ± 1.26 g). Average harvested biomass from raceways was 57.33 kg/m3 with an average daily weight gain per fish of 4.47 g per day. On the other hand, average harvested biomass from control ponds was 0.38 kg/m3 with an average daily weight gain per fish of 4.60 g per day. Average feed conversion ratio (FCR) in both raceways and control ponds was recorded as 1.25 and 1.24, respectively. Overall survival rate in both raceways and control ponds was above 99%. No sign of any disease was noted at any stage in both study groups. Crude protein and fats contents did not reduce in any raceway despite of high stocking density and sharp seasonal changes. Profile of essential and non-essential amino acids were found to be upto nutritional requirements of adult human. High levels of n-3 and n-6 fatty acids in fish collected from raceways as compared to those in traditional earthen pond show that muscle quality was not compromised due to high stocking density in small area. Return on investment excluding capital cost was 47.05 which implies that IPRS technology can be economically feasible with further modifications.

The effects of stocking density on growth performance, serum biochemistry, digestive enzymes, immune response, and muscle quality of largemouth bass (Micropterus salmoides) reared in nine in-pond raceway systems (IPRS, 22.0 m × 5.0 m × 2.0 m) were studied. M. salmoides with initial an body weight of 8.25 ± 0.51 g and body length of 6.99 ± 0.44 cm were reared at an initial stocking density of 90.91 ind./m3 (low stocking density, LSD), 113.63 ind./m3 (middle stocking density, MSD), and 136.36 ind./m3 (high stocking density, HSD) with triplication. After 300 days of culture, MSD recorded the highest final body weight, weight gain, specific growth rate, and yield, but the food conversion ratio in MSD was the lowest. The viscerosomatic index in LSD was significantly higher than other groups. The fish serum reared at HSD showed significantly lower total protein, higher total cholesterol, triglyceride, total bilirubin, glucose content, alanine transaminase, and aspartate transaminase activity. Significantly lower intestinal amylase, lipase, trypsin activities, hepatic superoxide dismutase (SOD) and catalase (CAT) activities, and higher malondialdehyde content were detected in HSD compared to others. The content of crude lipid, saturated fatty acid decreased, and total essential amino acid, delicious amino acid, and polyunsaturated fatty acid increased in muscle with stocking density increase. No significant difference was observed in muscle texture. Profitability analysis indicated the benefit-to-cost ratio varied between 1.10 and 1.68, of which MSD was significantly higher than others. The optimal stocking density for M. salmoides should be 113.63 ind./m3 in an IPRS farm.