The accumulation of organic waste such as aquatic animal feces or uneaten feed leads to the deterioration of water quality in aquaculture systems.
Various investigations have reported that when fish are confronted with ammonia, there is an increase in ammonia in the blood and deterioration of muscle quality.
Muscle texture is a predominant determinant of quality and is the most important organoleptic characteristic of muscle. Taste is another important quality criterion, which is made up of free amino acids.
A team of researchers from the Hubei Academy of Agricultural Sciences and Yangtze University investigated ammonia stress on antioxidant system responses, lipid metabolism, and muscle quality in rainbow trout (Oncorhynchus mykiss).
Ammonia levels in the water
The investigators used ammonia concentrations of 0 (control group), 10 mg/L (T1), 20 mg/L (T2), 30 mg/L (T3), 45 mg/L (T4), and 60 mg/L ( T5).
“Blood ammonia content in a dose-dependent manner after TA-N treatment indicates that the ammonia stress model was successfully established,” they describe.
They added NH4Cl, ice, and oxygenation to the water to regulate the ammonia concentration, water temperature, and dissolved oxygen. During the exposure of the fish to ammonia, the indicators of these parameters were monitored every 15 minutes.
In addition, the researchers took blood samples from the tail vein to determine the concentrations of ammonia and cortisol in the blood.
Effects of ammonia on the quality of trout
According to the study results, exposure to lower ammonia concentrations (less than 30 mg/L) with changes in EPA and DHA content, while significant decreases were observed at ammonia concentrations higher than 30 mg/L.
“Exposure to ammonia degrades the quality of meat. The deterioration of the quality of the muscle could be related to the decrease of the water absorption capacity of the myofibrils to interfere with the collagen and the matrix of myofibrils”, they report.
Also, the results of the study showed that the ammonia content in the blood and the relative fluorescent expression of the ROS content were significantly increased, indicating the existence of oxidative stress in trout after ammonia treatment.
Conclusion
“Ammonia stress impairs muscle qualities, leading to impaired color, texture, odor, and flavor,” they conclude.
They also highlight that the results are important to establish the relationship between muscle quality, lipid metabolism and environmental adaptability of rainbow trout.
The study was funded by the National Key R&D Program of China, China Agriculture Research System and Young Top notch Talent Cultivation Program of Hubei Province.
Reference (open access)
Wu, Yiwen and Zhao, Manman and Xia, Yuting and Sun, Weiqing and Xiong, Guangquan and Shi, Liu and Qiao, Yu and Wu, Wenjing and Ding, Anzi and Chen, Lang and Wang, Lan and Chen, Sheng, Deterioration of Muscle Quality Caused by Ammonia Exposure in Rainbow Trout (Oncorhynchus Mykiss). Available at SSRN: https://ssrn.com/abstract=4363148 or http://dx.doi.org/10.2139/ssrn.4363148
