Abstract

All metazoans have an innate immune defence mechanism however the adaptive immune system’s components first arise in the jawed vertebrates known as the gnathostomata. Therefore, fish are the first animal phylum to have both an innate and an adaptive immune system, making them particularly interesting for immune system developmental studies. Studies of the fish immune system and defence against diseases frequently linked to intensive fish rising have received more attention as a result of the significant expansion in aquaculture in recent decades. The primary elements of the fish’s innate and adaptive immune system are discussed. When it comes to immunological defence in fish, the innate characteristics are at the forefront and play a critical role in disease resistance. Although the fish’s adaptive response is frequently delayed, it is crucial for long-lasting immunity and a crucial component of a successful vaccination. The primary fish diseases are described, the pathogenicity and host defence are reviewed, and several internal and environmental elements that can influence a fish’s immune system are covered. The key preventive methods, such as immunisation, probiotics, and immunostimulation, are discussed. The wide variations in disease susceptibility and immune defence among various fish species, which are a result of the lengthy evolutionary separation of modern teleosts, are a crucial factor in the immunological regulation of fish diseases. The utilisation of molecular and proteomic technologies in future research is likely to help with disease resistance breeding programmes as well as the investigation of crucial immune defence and preventative measure components.