The Distrito Federal (DF) is a Brazilian federative unit made up of a single municipality, Brasília, the capital of Brazil, which is among the Brazilian cities with the largest number of tilapia farms (Brasil, 2023). The DF’s aquaculture production data is estimated at 2,200 tons/year, with tilapia accounting for over 88% of this amount (Seagri, 2024).
The study’s target population consisted of all commercial tilapia farms (n=112) registered with the animal health service of the Distrito Federal’s Secretariat of Agriculture (SEAGRI), identifying three commercial production typologies: 1) hatchery (breeding) or alevin sales establishments; 2) commercial fattening farms (grow-out) subdivided into 2-a) closed system fattening farms and 2-b) semi-closed system fattening farms and 3) recreational fishing establishments ("pay-to-fish"). The answers to the questionnaire were used to categorize the fish farms in terms of their degree of vulnerability to the introduction and spread of pathogens. Two point tables with 15 check items each were used to determine each farm’s score. The farms were classified from A to D (insignificant, low, moderate and high risk) in terms of their biosecurity level (BL). In addition, atypical health events (mortalities) were investigated over a 12-month period, using an instant messaging app (WhatsApp®).
Only 2 farms were considered class A, while 39, 53 and 18 farms were classified as B, C and D, respectively. The group of farms made up of pay-to-fish farms had the highest score, representing the stratum with the greatest potential risk of introducing and especially spreading diseases. It was found that the safest farms are the fattening farms with closed cultivation (BL=5.83, SD=1.47), followed by young fish farms (BL=8.00, SD=1.46) and semi-closed fattening farms (BL=8.24, SD=2.20). It was found that there was a statistically significant difference (p<0.05) between the variables of some groups, as illustrated in Fig 1. The typology of fattening farms in a closed system scored better than the semi-closed fattening and pay-to-fish groups in terms of the vulnerability level (VL) and BL, although there was no statistical difference between the groups when assessing only the risk of dissemination (RD).
A total of 27 health events were investigated, 20 of which occurred during the autumn and winter periods.
Considering the occurrence by strata, 55.5% (15/27) of the events took place in fattening farms, 25.9% (7/27) in young form farms and 18.5% (5/27) in pay-to-fish farms. Water and fish analyses (histopathology, qPCR and RT-qPCR) were conducted at UnB and UFMG to search for pathogens such as Tilapia Lake Virus, Megalocytivirus pagrus 1 (Infectious Spleen and Kidney Necrosis Virus - ISKNV) and other viral, bacterial and parasitic diseases. Only 3 farms tested positive for officially controlled diseases in Brazil: ISKNV (n=1) and Francisellosis (n=2). Farms with a C classification that transited interstate.
The method adopted (consisting of a questionnaire, individual categorization of production units, evaluation of mortalities and classification of risks by production strata) also provided valuable information for the DF’s veterinary service, which can subsequently draw up a surveillance plan focused on farms and production strata with the highest health risk. In addition, we believe that this model can be used for risk management both by private companies that integrate different tilapia farms and by veterinary services in other states and countries with more representative tilapia production.