Pangasius pleurotaenia occurs throughout the survey area, from the northern station of Chiang Saen to the Mekong delta, although apparently the species is rare both in the far north and far south.

According to Rainboth (1996), this species prefers greater water clarity than most other pangasiids and, based on the size of its eyes, it may rely more on its vision for catching its prey than other pangasids. Many fishermen (i.e., at least seven fishermen from Thailand and the Lao PDR) mentioned that the occurrence of Pangasius pleurotaenia coincides with high incidence of certain insects near the water surface, in particular dragonflies. Some of the same fishermen said they had observed the fish coming to the surface to catch insects, confirming that the species relies on vision to catch its prey.

Below the Khone Falls, Pangasius pleurotaenia migrates upstream at the beginning of the dry season, a movement that continues in waves until March. These migrations are triggered by receding/low water levels. Late in the dry season, probably induced by the first rain showers, the species migrates downstream from the Khone Falls, at least as far as Kandal province. Migratory behaviour in the Mekong delta appears to be less clear, and none of the fishermen in that area reported any migratory activity by Pangasius pleurotaenia.

Along the stretch from Khone Falls and up to Chiang Rai Province, the first heavy rains, marking the end of the dry season, triggers Pangasius pleurotaenia to migrate upstream.. From the Khone Falls to Loei province in Thailand, the migration occurs over a relatively short period, typically during May-June. Further upstream, from Xayaboury to Chiang Rai, the migration tends to take place over a longer period, from March to August.

Several fishermen in Thailand and the Lao PDR reported that Pangasius pleurotaenia migrates into tributaries and small streams. One fisherman stated that it spawns in tributaries.

Reports of eggs being observed were made in March (1 report), April (4), May (11), June (12), July (4), August (2), September (1), October (1), November (1) and December (1). One fisherman in Stung Treng province, near the Khone Falls, observed eggs twice per year, during May-June and November-December. Based on these observations, the peak spawning period can be taken as May-June, coinciding with the onset of the flood season.

Pangasius pleurotaenia has previously been identified in the tone trap fishery at the Khone Falls, which targets highly migratory small cyprinids during the dry season from January to March (Baird, 1998). Singanouvong et al. (1996b) also sampled the species during the flood season over a three-year period and found that most migratory activity took place when the water flow volume was increasing rapidly. That increase occurred within a short time span, from early to mid-June in all three years.

 

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