Daily otolith ring validation, age composition, and origin of the endangered striped catfish in the Mekong

Abstract

The endangered striped catfish, Pangasianodon hypophthalmus is a large-bodied, migratory catfish, and one of the most cultured catfishes in the world. This study examines the otoliths of drifting wild-caught and hatchery-raised larvae of striped catfish to validate daily ring counts, calculate fish age, and estimate spawning time and spawning location to improve our understanding of the species’ life history. We conducted daily sampling of larval/juvenile striped catfish in the Mekong mainstream in Phnom Penh in 2015 and at a fish hatchery in Cambodia. Daily water levels and river distances at and between four hydrological gauges over the Mekong River reach between Phnom Penh and Cambodia-Lao border were also collected. Standard length and otolith ring counts were examined in both hatchery-raised (150) and wild-caught (390) samples. This study revealed that (i) mass larval drift of striped catfish at the Mekong River in Phnom Penh took place from July 13th to July 23rd, 2015 corresponding with increasing flow, (ii) otolith rings are formed daily in hatchery-raised larvae, and can be used to determine the age of wild larvae/juveniles, (iii) otolith ring increments are strongly correlated with standard length in hatchery-raised larvae, but not in wild-caught larvae, (iv) mean standard length and age of striped catfish larvae collected in Phnom Penh are 14.65 mm (se = 0.07) and 27.6 days (se = 0.13), respectively, and (v) most striped catfish likely spawn in June and early July between the full and new moon, and the spawning grounds are most likely located along the Cambodian Mekong between Stung Treng and Kratie and, in 2015, travel time from spawning grounds to Phnom Penh was approximately 27 days. Upper Cambodian Mekong River is therefore likely very necessary for the persistence of all striped catfish populations and fisheries in the lower floodplains of Cambodia and Mekong delta. The existing and proposed dams in the upper Mekong River in Cambodia and beyond would drastically affect spawning sites and dry season refuge habitats and disconnect the upstream spawning from the downstream rearing habitats of the species.