Abundance of wild Nile tilapia (Oreochromis niloticus) around cages at source of the Nile fish farm: implication for disease transmission between farmed and wild fishes

Abstract

Although tilapia culture in cage fish farming systems in Uganda presents a steady rise in growth the entire sector is a subject to the different emerging tilapiine diseases and pathogens which have so far been reported at different fish farms by farmers and researchers to cause significant stock depreciation through increased fish mortalities arising from disease and pathogen infestation to the cultured stocks. Currently, with the increased intensification, production and commercialization of the fish culture systems, there have markedly been increased concerns of rampant disease outbreaks among cultured tilapiine stocks pertaining the outbreak and emergence of bacterial, fungal and viral diseases as well as parasite infestation which has hindered investment, thus curtailing unimpeded production and extension of the sector. Despite the conducive tropical climate that favors fish farming in the tropics, limited, if any, focus has been invested as regards fish health and the subsequent biosecurity programs meant to protect fish from contracting infections therefore inferring increased disease infestation and hindered sector growth. Attention as pertains fish health and biosecurity measures have long been focused on the indirect modes of disease and pathogen transmission (transfer of infectious agents from reservoirs to the fish hosts by inanimate objects [e.g., vehicles and PPE], or animate intermediaries). Despite the practice of such measures to combat disease infestation onto the farmed stocks, the prevalence of diseases and pathogens is persistent thus farmers and researchers have still reported increased cases of disease outbreak among farmed fish stocks. However, the design, construction and positioning of the cages systems in water bodies infers to easily permit the interaction of wild and farmed fish stocks thus facilitating direct transmission of disease pathogens and parasites from the wild to the farmed fish stocks or vice versa. The results of this study validated that wild fish populations lied in proximities of fish cages and are capable of transmitting infectious agents to farmed tilapiine stocks or vice versa. Therefore, besides the indirect modes of transfer of infectious agents that are affirmed to attribute to the rampant disease prevalence amongst farmed tilapiines, the results of this study call for further interventions by researchers and farmers as regards prevention of direct disease and pathogen transfer modes between wild and farmed tilapiines. Finally, the review contains suggestions for future research that will fill gaps needed to effectively prevent, manage and combat rampant disease incidences on fish farms.