Brackish water reduces tilapia transport stress

Adding 4 grams of salt to each litre of water used when transporting tilapia reduces stress, liver damage, oxidative stress and hydromineral imbalance, according to a new study.

Tilapia can adapt to a range of salinity levels © Gardfisk

Biologists from the Peoples’ Friendship University of Russia (RUDN University), the Iranian Fisheries Sciences Research Institute, the Federal Institute of Education, Science and Technology Catarinense, and the Gorgan University of Agricultural Sciences and Natural Resources evaluated the effects of adding different doses of salt (0, 2 and 4 g/L) to transport water had on stress and antioxidant parameters of Nile tilapia (Oreochromis niloticus), after 3 hours of transport.

Previous studies regarding the application of salt in transport water have revealed that adding 1 and 2 g/L of salt decreases bacterial load, and 4 and 8 g/L increase survival in the transport of Nile tilapia. However, according to the researchers, there were no data on the benefits of salt on stress, hydromineral balance and antioxidant capacity in Nile tilapia.

One of the bottlenecks in the transport of fish is the deterioration of water quality, which is dangerous for fish. The stress caused by transport increases the metabolic rate, oxygen consumption and ammonia excretion. Therefore mitigation of stress during transport can reduce the deterioration of water quality, although the researchers reported that adding salt to the water did not bring benefits with respect to dissolved oxygen and ammonia levels in the water.

However, the addition of 2 or 4 g/L of salt to the water reduced cortisol and/or glucose elevations, suggesting a stress-relieving effect. Likewise, the results of the study indicate that the addition of 4 g/L of salt to the water can reduce stress in Nile tilapia during transport.

However, the study suggests that it doesn't improve overall water quality © RUCN University

"The current results suggest that the addition of salt to the water may reduce osmotic disturbance in fish, which is likely due to the lower osmotic gradient between the fish body and the surrounding water," they explained in a press release.

Antioxidant enzymes and non-enzymatic antioxidants protect cells from the adverse effects of oxidative stress produced by excess reactive oxygen species and are often increased after a stressful event.

In general, the antioxidant parameters show that the addition of salt to the water can reduce the oxidative condition during fish transport.

"The addition of salt to the water (particularly 4 g/L) can suppress the negative effects of transport-induced oxidative conditions in fish liver tissue. Less oxidative conditions lead to greater liver cell integrity and higher hepatic ALT and AST concentrations," they report.

"The representative results indicated that adding salt to the water has benefits for the transport of Nile tilapia. Fish transported in brackish water present a lower degree of stress, less liver damage, less hepatic oxidative stress, and better hydromineral balance, although there is no benefit in regarding the quality of the water" they conclude.

Click here to access the study, which was published in Aquaculture Reports, 27, 101378.