Pacific white shrimp (Penaeus vannamei) are one of the most widely farmed species globally, and biofloc technology (BFT) systems have emerged as an innovative solution for more sustainable and intensive production. This system is based on the recycling of nitrogenous compounds, such as ammonia, which are converted into nitrate by a nitrification process carried out by bacteria. However, nitrite is an intermediate product in this cycle and, if its levels increase, it can become toxic to shrimp.
Nitrite spikes are a common and recurrent problem in biofloc systems, especially during the initial maturation phase of the culture. These spikes can last from 5 to 30 days, a period that often exceeds safe recommended levels and can seriously affect shrimp health and performance.
While the acute toxicity of nitrite has been well-studied, less is known about the effects of chronic or prolonged exposure, and more importantly, whether shrimp can recover from this stress. For this reason, a team of researchers from the Federal University of Rio Grande and the Alfred Wegener Institute set out to evaluate the impact of chronic nitrite exposure on the growth and immune response of P. vannamei and, in turn, to investigate its capacity for recovery. The goal was to determine which concentrations and durations of exposure are tolerable for the species without significantly compromising production.
Key findings
- Chronic exposure to high nitrite levels (three times the recommended safe level) causes high mortality in Pacific white shrimp, regardless of the exposure time.
- Shrimp can tolerate exposure to nitrite levels up to twice the safe limit for a period of up to 14 days without a significant reduction in survival.
- After a period of nitrite stress, surviving shrimp showed a remarkable capacity for compensatory growth, with growth rates returning to normal once nitrite levels were controlled.
- Nitrite exposure suppressed the shrimp’s immune response, as evidenced by a reduction in granular hemocytes. However, this immune function recovered upon restoration of optimal system conditions.
- The study provides a practical guide for producers: in biofloc systems, nitrite exposure should be limited to a maximum of twice the safe level (30.4 mg/L NO_2-N at a salinity of 25 g/L) for no more than 14 days to avoid production losses from mortality.
Study methodology: How the shrimp were stressed
To address this question, the researchers conducted a factorial experiment, subjecting the shrimp to different levels of nitrite stress. The study was divided into two phases: a stress phase and a recovery phase.
In the stress phase, P. vannamei juveniles were exposed to two elevated nitrite concentrations: twice (30.4 mg/L NO_2-N) and three times (45.6 mg/L NO_2-N) the recommended safe level, at a salinity of 25 g/L. The exposure was maintained for three distinct periods: 7, 14, and 21 days. A control group was kept at very low nitrite levels (less than 25% of the safe level).
After each stress period, the shrimp moved to the recovery phase, where they were transferred to a stable, healthy biofloc system with controlled nitrite levels. The total experiment lasted 49 days, allowing researchers to evaluate whether the shrimp that survived the stress could recover their growth and health.
The researchers monitored zootechnical parameters such as survival, weight, and growth rate, as well as immune health through a differential hemocyte count, which are the blood cells that play a crucial role in shrimp defense.
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Compensatory growth and immune recovery
The study published in the Journal of the World Aquaculture Society yielded significant results with direct implications for shrimp producers using biofloc systems.
High nitrite levels cause mortality, but shrimp show resilience
Exposure to the highest nitrite concentration (three times the safe level) resulted in high mortality across all exposure periods (7, 14, and 21 days), suggesting that this level should be avoided at all costs. However, shrimp exposed to twice the safe level did not experience a reduction in survival during the first 7 and 14 days. Survival only decreased by 23% when the exposure was extended for 21 days at the same level.
These findings are crucial for production management. In the recovery phase, the surviving shrimp showed a remarkable capacity for growth. Despite the initial adverse effects, growth parameters like weight gain and weekly growth rate (WGR) recovered and resembled those of the control group. Although some treatments did not reach the final weight of the control, the results demonstrate the shrimp’s ability to return to a normal growth pace once optimal water conditions are restored.
Nitrite affects immunity, but the biofloc system aids recovery
The study also evaluated the impact of nitrite on the shrimp’s immune response. It was found that all treatments exposed to high nitrite levels, regardless of concentration or duration, suffered a significant decrease in the percentage of granular hemocytes, which are the most important immune cells. This decrease suggests a suppression of the immune system, which could make the shrimp more susceptible to diseases.
Fortunately, at the end of the recovery period, the percentage of granular hemocytes increased in all previously affected treatments. The values returned to the range observed in healthy shrimp, indicating that the animals that survived chronic nitrite exposure recovered a part of their immune capacity. The researchers suggest that this recovery may have been driven by the biofloc system, which is known to be an immunostimulatory environment due to its rich microbial diversity.
Conclusions and recommendations for the industry
This study provides strong evidence that Pacific white shrimp possess considerable resilience to chronic nitrite exposure. Although high concentrations and prolonged periods can be harmful, the shrimp demonstrated the ability to recover their growth and immune function once nitrite levels were controlled.
For producers working with BFT systems, where nitrite spikes are difficult to avoid during the establishment phase, the study offers a clear recommendation: limit exposure to a maximum of twice the safe level (30.4 mg/L of NO_2-N at a salinity of 25 g/L) for a period not exceeding 14 days. With this strategy, a significant loss of survival can be avoided, and the shrimp will be able to grow normally after the stress period ends.
In short, proactive management of nitrite levels and an understanding of the shrimp’s capacity for recovery are key to success in intensive aquaculture production. The biofloc system not only offers sustainability benefits but can also act as an ally in the recovery of shrimp from environmental stressors.
Contact
Elisa Prates
Estação Marinha de Aquacultura, Universidade Federal do Rio Grande
Rua do Hotel, n°2, Rio Grande, RS 96210-030, Brazil.
Email: elisa7andrade@gmail.com
Reference (open access)
Prates, E., Saborowski, R., Damasceno, J., Holanda, M., Monserrat, J. M., Slater, M., & Wasielesky, W. (2025). Compensatory growth and nitrite management in the Pacific white shrimp (Penaeus vannamei) cultured in biofloc system. Journal of the World Aquaculture Society, 56(4), e70052. https://doi.org/10.1111/jwas.70052
Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.
