Toxic Effects on Bioaccumulation, Hematological Parameters, Oxidative Stress, Immune Responses and Tissue Structure in Fish Exposed to Ammonia Nitrogen: A Review.

Zhenkun Xu,Weiqiang Qiu,Jing Xie,Xiaoming Qin,Jun Mei,Jie Cao

doi:10.3390/ani11113304

Abstract

Simple SummaryAmmonia nitrogen is a common environmental limiting factor in aquaculture, which can accumulate rapidly in water and reach toxic concentrations. In most aquatic environments, fish are vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. It has been found that the toxic effects of ammonia nitrogen on fish are multi-mechanistic. Therefore, the purpose of this review is to explore the various toxic effects of ammonia nitrogen on fish, including oxidative stress, neurotoxicity, tissue damage and immune response.Ammonia nitrogen is the major oxygen-consuming pollutant in aquatic environments. Exposure to ammonia nitrogen in the aquatic environment can lead to bioaccumulation in fish, and the ammonia nitrogen concentration is the main determinant of accumulation. In most aquatic environments, fish are at the top of the food chain and are most vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. In fish exposed to toxicants, ammonia-induced toxicity is mainly caused by bioaccumulation in certain tissues. Ammonia nitrogen absorbed in the fish enters the circulatory system and affects hematological properties. Ammonia nitrogen also breaks balance in antioxidant capacity and causes oxidative damage. In addition, ammonia nitrogen affects the immune response and causes neurotoxicity because of the physical and chemical toxicity. Thence, the purpose of this review was to investigate various toxic effects of ammonia nitrogen, including oxidative stress, neurotoxicity and immune response.

Highlights

IntroductionThere are two main reasons for the growth of the mass concentration of ammonia nitrogen in farming water: one is the decomposition of organic matter containing nitrogen such as feed residues and aquatic animal excreta [3]
Ammonia accumulation in fish tissues disturbs circulatory systems and various hematological parameters related to lipid metabolism, immune defense system, blood coagulation and molecular transport
Ammonia accumulation leads to the activation of antioxidant enzymes such as superoxide dismutase (SOD), CAT and Thiobarbituric reactive substances (TBARS)

Summary

Introduction

There are two main reasons for the growth of the mass concentration of ammonia nitrogen in farming water: one is the decomposition of organic matter containing nitrogen such as feed residues and aquatic animal excreta [3]. Non-ionic ammonia has good lipid solubility and carries no electric charge, making it more fuse with the phospholipid bilayer on the cell membrane, diffusing through the cell membrane to the hemolymph and increasing the concentration of ammonia nitrogen in fish, producing toxic effects [7]. It can diffuse into fish through cell membranes, causing damage to important organs, including gill tissue, resulting in respiratory difficulties and reduced feeding rate of fish, and inhibiting their growth and development [8].

Bioaccumulation

Hematological Parameters

Oxidative Stress

Immune Response

Tissue Structure

Conclusions