The strategic use of water additives for tambaqui Colossoma macropomum transport: New insights of bacteriosis and productivity approach

The transport of live fish is a major sanitary issue for aquaculture. This study addresses two critical steps regarding natural recurrent mortality outbreaks after transport of tambaqui Colossoma macropomum. At first, five mortality outbreaks post-transport of juveniles showing clinical signs suggestive of columnaris were investigated. Flavobacterium columnare was ascertained as the etiological agent in all outbreaks, causing massive mortality up to 72 h after transport. Based on these findings, the next step consisted of a trial to investigate the use of three additives (8 g/L sodium chloride, 11.12 mg/L Melaleuca alternifolia essential oil and 60 mg/L oxytetracycline) in the water of transport, simulating fish farmers' practices to prevent disease outbreak. Juveniles (≅ 8 cm) were transported for 3 h under trade-mimicking conditions, then transferred to 20 tanks (5 groups, 4 replicates) and monitored for 30 days for analysis of health status. Zootechnical parameters (weight gain, total feed intake, feed conversion, specific growth rate and growth analysis) were assessed on days 1, 15 and 30. The best health status was attributed to the group transported with 0.8% NaCl, which showed 100% survival, in addition to being the only group that did not show behavioral changes and clinical signs, indicating the absence of any infectious biological source after transport. A poly-infection (Aeromonas jandaei and F. columnare) was detected in fish from all other groups (M. alternifolia, oxytetracycline and control). Furthermore, fish exposed to sodium chloride showed better weight gain and feed conversion compared to those transported with oxytetracycline (p ≤ 0.05). Then, the pathogenicity of the two isolated strains (A. jandaei and F. columnare) was ascertained by Koch's Postulate assay, which established two emerging pathogens for C. macropomum. This study addresses fundamental information for the development of fish farming and suggests the addition of salt at 0.8% in the water of transport to prevent columnaris and motile Aeromonas septicemia (MAS) associated disease.