**2. Materials and methods**

**1. Introduction**

94 Aquaculture - Plants and Invertebrates

and their management.

Prawn such as *Macrobrachium vollenhobenii* is an important source animal protein that provides good quality protein and essential minerals and vitamins. It is also regarded as safest animal source of protein which comes from either wild or culture system. The current decline in the status fish from wild has been attributed to overfishing, illegal and irresponsible fishing, habitat destruction and pollution, among other factors. More so, the increase in population and change in the consumption pattern of fish has create huge gap between the demand and supply of fish [1]. One of the ways to bridge this gap is through aquaculture. The act of aquaculture means rearing of aquatic organisms, which entails any form of intervention to improve the production quantity and quality, management, disease prevention and control.

Over the years, aquaculture has become the fastest growing sector in the world [2].

Worldwide total crusteceans was 6,915,100 tonnes representing about 7% of total aquaculture production [2]. This achievement was attributed to transformation of farming techniques from simple methods to an improved and intensive aquaculture which promotes high seed quantities, adequate knowledge of stocking density, supply of required fish feeds. However, in spite of the success recorded in the prawn farms in recent times, the performance are far from it demand. The poor performance has been associated with many constraints, such as, modern knowledge in the science of fish farming, government policy, fish feed industry, marketing, distribution, and diseases. One of the major barriers to prawn farming are diseases

Disease is an establishment of pathogens in prawn tissues which cause disorderliness in physiological function of the fish that result in physical, biological and economical losses. Diseases arise as a result of complex interaction among the fish, pathogen and culture environment [3, 4]. Fish has inbuilt immune systems and defence mechanisms which protect them from being infected with pathogens. But practice of intensive farming system has the possibility of exposing prawn to infections. However, bacteria have been reported to be responsible for about 70–80% of disease infection in fish [5]. Some important bacteria in prawn farming are *Pseudomonas aeruginosa* and *Aeromonas hydrophila. Pseudomonas aeruginosa* and *Aeromonas hydrophila* are gram-negative bacteria in the families of Pseudomonadaceae and Aeromonadaceae respectively. They are ubiquitous, facultative anaerobe, rod-shaped and sugar fermented organism. Studies have reported that *Pseudomonas aeruginosa* and *Aeromonas hydrophila* infection in fish has resulted into haemorrhagic,

The problems of increase antibiotic resistance bacteria, residual effect and environmental unfriendly experienced in the use of antibiotics could ameliorate by probiotics application. Therefore, current studies have moved toward search for alternative such as probiotics. Probiotics are life microbial feed supplements that improve health host by modify the gastrointestinal tract of the fish. Fish, being a hydrophilic animal rely solely on the environment (water) which filtering through the body and gill as fish performs it physiological function would benefit from use of probiotics. Probiotics enhance the nutrient utilisation, modulate gut flora, inhibit the growth of pathogenic bacteria and improve growth and immune system of the fish as reported in the previous studies [6, 7]. Several probiotics have been used in

speticemia, furunculosis and high mortality among others [1].
