According to the data gathered during the survey, Puntioplites falcifer is a common species in the Mekong mainstream all the way from Chiang Rai province in northern Thailand to the southernmost station in Viet Nam. Although relatively easy to identify because of its very long dorsal fin, it is possible that the identity of the species has been confused with other Puntioplites spp., especially P. proctozysron, which is another common species.

The maximum reported size was around 40 cm, which is slightly larger than the maximum size of 35 cm reported by Rainboth (1996).

Several fishermen mentioned that Puntioplites falcifer has a preference for deep pools in the river. It was also mentioned that the fish migrate to streams, canals and lakes during the flood season. The last statement is not in agreement with Rainboth (1996), who specifically stated that Puntioplites. falcifer has a preference for large rivers and avoids standing water. Puntioplites proctozysron, on the other hand, reportedly has a preference for lentic environments.

Puntioplites falcifer is a social species that migrates in large schools. It was also reported to migrate together with a number of other species, in particular Cosmochilus harmandi, Cirrhinus spp., Morulius chrysophekadion and Bangana sp.

It is difficult to summarise the migration patterns of this species because the migrations are spread out over a long period. However, it appears that the basin can be divided into four parts:

" Northern Lao PDR and Thailand (from Loei and Chiang Rai provinces). Upstream migrations there were reported to occur from February to May and July to August, but the main period of upstream migration is during March-April. Downstream migrations occur from September to November.

" Champassak (Lao PDR) to Nakhon Phanom province (Thailand). Upstream migrations are concentrated during May-June. Downstream migrations occurduring November-December.

" Northern Cambodia (Stung Treng to Kratie). Puntioplites falcifer was reported to migrate upstream in this river stretch during November-December, and downstream during April-June.

" The Mekong mainstream in Viet Nam. Only one report was received, from Tien Giang province, on upstream migration in July and downstream migration during October-December.

From Nong Khai to Thakhek, and from Kompong Cham to Tra Vinh in Viet Nam, no indications were given on the direction of the migrations. Similarly, no information was provided on the direction of migrations in the Bassac River.

A number of environmental factors and events have been connected with the migrations of this species, with some of them being, to a certain extent, contradictory. Fishermen at five stations in the Lao PDR, for example, mentioned that Puntioplites falcifer occur in large numbers when the water is reddish in colour, while fishermen at two other Lao stations mentioned that clear water is indicative of a high concentration of this species. Water level appears to be a very important factor, since migration activities of this species intensify when the level rises or falls.

Some fishermen reported that periods of upstream migration and good catches are associated with the occurrence of water temperature changes and strong winds. In Cambodia, both upstream and downstream migrations are associated with a full moon. One Thai fisherman in Mukdahan reported that Puntioplites falcifer attains sexual maturity at about 0.3-0.4 kg. In all four countries, eggs were reported during March-December, with most reports giving May-June as the peak period. However, there were many more reports from Cambodia than from the other countries. The reason could be due to the low occurrence of the species in the Mekong mainstream in the Lao PDR and Thailand during the spawning season. Juveniles measuring 2 cm were observed throughout the year, with peak occurrence from May to November. Vietnamese fishermen reported that Puntioplites falcifer spawnsin small streams and ricefields.

Hypothesis:
During the first heavy rains of the monsoon season, Puntioplites falcifer migrates to the nearest large tributary, and spawns in tributaries and canals and associated flood-plain areas. The juveniles spread out along the riverbank, and some of them enter the Mekong mainstream. When the river level falls, adult and juvenile Puntioplites falcifer move back to the Mekong River, where they stay in deep pools until the next flood season.

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