Balancing Food For Salty Water Growing

Jim Crocker
19th June, 2025

Balancing Food For Salty Water Growing

Compared to freshwater controls (A, a, B, b), saline-alkaline stress induced significant gill damage in Nile tilapia (Oreochromis niloticus), an effect that was visibly exacerbated in fish fed a high-protein diet, which showed severe red blood cell aggregation (D, d).

Image adapted from: Liu et al. / CC BY (Source)

Key Findings

  • Research from East China Normal University shows that harsh saline-alkaline waters severely stress Nile tilapia, damaging organs, increasing energy needs, and hindering growth
  • Feeding tilapia a diet with 27% protein and 35% carbohydrates significantly improved their growth and reduced stress in these challenging conditions
  • This optimal diet boosted beneficial gut bacteria and energy use, helping fish cope with stress and excrete ammonia more effectively
The global demand for food continues to rise, making the development of sustainable food sources crucial. Aquaculture, the farming of aquatic organisms, plays a vital role in meeting this demand. However, a significant challenge lies in cultivating fish in environments that are not ideal, such as saline-alkaline waters. These waters, characterized by high salt content and elevated pH levels, impose considerable stress on fish, impacting their growth and survival. Despite the potential for expanding aquaculture into these less-utilized areas, there is limited understanding of the specific nutritional strategies, particularly regarding protein and carbohydrate levels, required for fish to thrive under such conditions. Addressing this knowledge gap, recent research from the School of Life Sciences, East China Normal University[1], aimed to clarify how different protein-to-carbohydrate ratios in diets influence the adaptation of Nile tilapia (Oreochromis niloticus) to combined salinity-alkalinity stress. This study sought to provide theoretical support for developing specialized feeds for aquaculture in these challenging environments, ultimately contributing to global food security. Fish, like all aquatic organisms, must maintain a stable internal balance of water and salts, a process known as osmoregulation. Environments with fluctuating salinity, such as saline-alkaline waters, are particularly demanding. Fish that can tolerate a wide range of salinities are called euryhaline, and Nile tilapia are known to possess these adaptive capabilities. Their ability to dynamically adjust their osmoregulatory strategy, from actively absorbing salt in freshwater to secreting it in saltwater, is crucial for survival[2]. However, the stress imposed by not just salinity but also high alkalinity adds another layer of complexity. Previous studies have shown that multiple abiotic stresses, including salinity and alkalinity, significantly impact fish, leading to changes in their metabolic and molecular osmoregulation processes[3]. For instance, research on Mozambique tilapia (Oreochromis mossambicus) revealed that salinity, alkalinity, and combined saline-alkalinity stresses alter metabolic profiles in the intestine, affecting osmolytes (molecules used to balance internal fluid pressure), energy sources, and amino acids, and engaging pathways like the TCA cycle and glycolysis/gluconeogenesis, which are central to energy production[3]. Similarly, studies on Japanese medaka (Oryzias latipes) exposed to alkalinity stress showed widespread changes in gene expression in the gills, affecting pathways related to energy, ion regulation, and even suppressing the immune system and reproduction[4]. Another study specifically on Nile tilapia gills under alkaline water exposure found changes in genes related to stress response and energy metabolism, including nitrogen and sulfur metabolism[5]. These earlier findings underscore that saline-alkaline conditions demand significant energy and physiological adjustments from fish. In the East China Normal University study, juvenile Nile tilapia were fed one of three diets over 50 days. All diets provided the same total energy and fat content but varied in their protein-to-carbohydrate ratios: 27% protein with 35% carbohydrate, 35% protein with 25% carbohydrate, or 42% protein with 15% carbohydrate. Fish were then exposed to either normal freshwater or a saline-alkaline water environment (16.0 PSU salinity and 3.0 g/L sodium bicarbonate alkalinity). The researchers monitored growth performance, overall body composition, and the fish's antioxidant capacity, which indicates their ability to combat cellular damage. The results clearly demonstrated the detrimental effects of saline-alkalinity stress. Fish in these harsh conditions experienced oxidative stress, a state where there's an imbalance between free radicals and antioxidants, leading to cellular damage. Their gill tissues, vital for respiration and osmoregulation, showed structural damage, and liver cells exhibited cytoplasmic vacuolation, indicating cellular distress. This stress also increased the fish's energy demand, made them more susceptible to intestinal pathogens, and ultimately inhibited their growth. These observations align with the metabolic and stress responses seen in previous studies[3][4][5], highlighting the significant physiological burden these environments place on fish. Crucially, the study found that the diet containing 27% protein and 35% carbohydrate significantly improved the tilapia's ability to cope. Fish on this specific diet showed reduced oxidative stress, increased crude protein content in their bodies, and, most importantly, significantly improved growth performance even under long-term saline-alkalinity stress. To understand how this diet provided benefits, the researchers delved into the fish's intestinal microbiota and transcriptomics. Transcriptomics involves analyzing the complete set of RNA molecules in a cell, providing insights into which genes are active. The analyses revealed that the optimal diet (27% protein and 35% carbohydrate) fostered a healthier gut environment by increasing the abundance of beneficial bacteria, often referred to as probiotics. Furthermore, it upregulated energy metabolism pathways, particularly those related to glucose metabolism. This suggests that a higher carbohydrate content, within the tested range, provided a readily available energy source that helped the fish meet the increased energy demands of osmoregulation and stress response, as also indicated by earlier research on metabolic adjustments under osmotic stress[3][5]. The improved gut health, supported by beneficial microbes, likely enhanced nutrient absorption and overall resilience. This research provides valuable insights into optimizing nutritional strategies for aquaculture in challenging saline-alkaline waters. By identifying a specific protein-to-carbohydrate ratio that enhances tilapia's adaptability and growth under stress, the study offers practical, theoretical support for the development of the saline-alkaline water feed industry. This advancement is a step towards expanding the potential for aquaculture in diverse environments, thereby strengthening global food security and nutritional supply.

AgricultureNutritionAnimal Science

References

Main Study

1) Nutritional strategies for Nile tilapia: protein and carbohydrate balances in saline-alkaline aquaculture

Published 17th June, 2025

https://doi.org/10.1186/s40104-025-01215-8

Related Studies

2) Physiological mechanisms used by fish to cope with salinity stress.

https://doi.org/10.1242/jeb.118695

3) Metabolism responses in the intestine of Oreochromis mossambicus exposed to salinity, alkalinity and salt-alkalinity stress using LC-MS/MS-based metabolomics.

https://doi.org/10.1016/j.cbd.2022.101044

4) Transcriptomic profiles of Japanese medaka (Oryzias latipes) in response to alkalinity stress.

https://doi.org/10.4238/2012.June.15.2

5) Comparative transcriptome analysis of Nile tilapia (Oreochromis niloticus) in response to alkalinity stress.

https://doi.org/10.4238/2015.December.22.16


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