Over the past decade, invasive catfish Pterygoplichthys spp. spread throughout most of the river systems of Vietnam. One of the possible reasons for their rapid settlement is associated with the transit movements of armoured catfish through river estuaries and desalinated coastal zones. Employees of the laboratory of behavior of lower vertebrates (Ganzha E.V., Pavlov E.D.) together with a Vietnamese colleague (Tran Duc Dien) assessed the likelihood of estuarine dispersal of armoured catfish, both in situ and in office conditions.
Using control fisheries, it was established for the first time that armoured catfish are found in the waters of the Darang River estuary with salinity up to 25‰ inclusive. Previously, armoured catfish in brackish waters (up to 8‰) were found only in the rivers of Southeast Mexico (Capps et al., 2011).
The ability of armoured catfish to move and breathe in sea water (33‰) was experimentally assessed. Fish in the control group, placed in fresh water, were usually positioned motionless on the bottom. In seawater, on the contrary, fish more often moved both horizontally and vertically. The locomotor activity of fish in sea water began to decrease only at the 13–15th minute of the experiment. The presence of armoured catfish in sea water for the first 6 minutes led to disruption of respiratory movements (opening/closing of gill slits) in fish until they stopped, but did not have a significant effect on their motor activity.
The results of field and experimental studies indicate that invasive catfish can be found in river estuaries, move in them and at the same time are able to avoid water of high salinity due to directed movement into the surface, often desalinated layers of water. These facts are in good agreement with the hypothesis about the invasion of armoured catfish through river estuaries and sea coasts under concomitant favorable external conditions.
The work was carried out within the framework of the Ecolan 3.2 project (Russian-Vietnamese Tropical Center with financial support from the Russian Ministry of Education and Science) and the Russian Science Foundation grant No. 19-14-00015. The article was published in the journal Aquatic Invasions.
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