Aquaculture is the second-fastest-growing sector in the world after informatics and its. Average growth of aquaculture is annually ~8.8% over the last 30 years. Turkey has great potential in terms of fish production and the number of fish farms started to increase rapidly. Fish production in intensive culture conditions has enlarged possible threats of contagious disease outbreaks due to high stocking densities, water quality or environmental gradient, etc., as well as the combination of all these factors together. Depending on animal husbandry situations and organizational conditions, gradation of the aquatic surroundings and outbreaks of bacteriological diseases may well cause production losses around 30-40% in aquaculture facilities. Some fish diseases reported most repeatedly in Turkish aquaculture facilities are Vibriosis, Furunculosis, Streptococcosis, Lactococcosis, Aeromonas septicemia, Yersiniosis, Photobacteriosis and Flavobacteriosis. Antibiotics, disinfectants and chemotherapeutics used for the prevention and treatment of diseases result in residual antibiotics and chemicals in fish products, microorganisms resistant to antibiotics and damages to the aquatic environment and human health. This situation has led researchers to use alternative feed additives in fish diets such as medicinal plant, herbal extracts, phytochemicals, plant secondary metabolites, immunostimulants and probiotics. This review includes research conducted in Turkey between the years 2001 and 2020, and aims to summarize the findings regarding the use of medicinal plant, herbal extracts, phytochemicals, plant secondary metabolites and immunostimulants in fish feed to prevent and treat diseases, improve immunity, increase disease resistance, and reduce stress in fish towards a better management and best aquaculture practice for the sustainability of the growing aquaculture industry in the region and worldwide.

This study was performed to determine the effects of the extracts of two alternative antimicrobial agents that do not harm the ecosystem (rosemary, Rosmarinus officinalis and aloe vera, Aloe barbadensis) when added to the feed of tilapia (Oreochromis niloticus) on the growth performance, proximate composition, and biometric characteristics. Rosemary extract was added to the experimental diet in ratios of 0.1%, 0.25%, and 0.5% while aloe vera extract was added to the experimental diet in ratios of 0.5%, 1%, and 2.5%. After 90 days of the feeding trial, no change was seen in the weight increase, specific growth rate, feed conversion ratio, condition factor, hepatosomatic index, or viscerosomatic index of the tilapia. The fact that proximate analyses did not differ between groups showed that the plant extracts did not adversely affect the health status of tilapia in the ratios used in this study. As a result, the addition of 0.1%, 0.25%, and 0.5% rosemary extract and the addition of 0.5%, 1%, and 2.5% aloe vera extract to tilapia feeds did not cause changes in the growth performance, biometric indexes, or chemical composition findings of the fish meat.