Zeb Hogan

Homogenization of California’s Fish Fauna Through Abiotic Change

The decline of native fish populations and the invasion of non-native fishes are the most noticeable trends in Californias freshwater fish assemblages over the last century (Moyle and Williams 1990, Moyle 2000). Moyle (2000) and Dill and Cordone (1997) date the first introduction of non-native fish into California back to the latter half of the 19th Century. Yoshiyama et al. (1998) place the beginning of the decline of the states chinook salmon populations also near the turn of the century. The mid-1800s also marks the beginning of a population explosion in California, driven by the discovery of gold in the Sierra Nevada in 1848.

The Imperiled Giants of the Mekong

Southeast Asia’s Mekong river supports a vast freshwater fishery. One of the species caught by local fishers is the Mekong giant catfish (Pangasianodon gigas), which according to The Guinness Book of World Records is the planet’s largest freshwater fish: It can measure 3 meters long and weigh 300 kilograms. But fewer and fewer examples of this huge fish have turned up in nets recently, and last year the World Conservation Union added this catfish to its list of critically endangered species. Although the loss of this charismatic fish would be a tragedy in itself, the plight of the Mekong giant catfish also highlights the precarious position of other Pangasiid catfish species inhabiting the Mekong river. Hogan and his colleagues explain their efforts to understand the migratory behavior of these fish in hopes of improving the chances for their long-term conservation.

Threatened fishes of the world: Probarbus jullieni Sauvage, 1880 (Cypriniformes: Cyprinidae)

Common names: Seven-striped barb (E), Jullien’s golden carp (E), Pla Isok (Thai), Trey Trawsak (Khmer), Pa Eun Ta Deng (Lao). Conservation status: Endangered (Baille and Groombridge 1996). CITES Appendix I (1975). Schedule two protected species in Laos (Baird 2006). Identification: Large pharyngeal teeth in single row; only maxillary barbels; dorsal fin with one spine and nine branched rays; five branched anal rays; five longitudinal stripes above lateral line (Roberts 1992). Maximum total length 165 cm and weight 70 kg (Baird 2006). Distribution: P. jullieni once occurred in the Mekong, Chao Phraya, Meklong, Pahang, and Perak River Basins in Thailand, Laos, Cambodia, Vietnam, and Malaysia (Roberts 1992). Abundance: Self-sustaining populations of P. jullieni may no longer occur in the Chao Phraya or Meklong Rivers, but are found in the Mekong Basin (Roberts 1992). In the Pahang Basin, it is extirpated or rare. Populations have declined in the Perak Basin due to hydropower development (Baird 2006). Populations in Laos have declined significantly (Baird 2006). Habitat and ecology: Adult P. jullieni prefer mainstream habitats; juveniles sometimes enter floodplain habitats. P. jullieni feeds on zooplankton, aquatic plants, fruits, and aquatic invertebrates (Poulsen et al. 2004). Reproduction: In the Mekong River Basin, P. jullieni spawns during the dry season between November and February. Artificial breeding for aquaculture occurs in Laos and Thailand using wild stock (Poulsen et al. 2004; Baird 2006). Threats: Large-mesh gill netting at spawning sites, hydrological changes, and habitat fragmentation (Baird 2006). Conservation action: The government is regulating large-meshed gill net use in northeastern Cambodia. P. jullieni benefited from conservation zones in southern Laos (Baird 2006). Conservation Environ Biol Fish (2009) 84:291–292 DOI 10.1007/s10641-008-9418-7

Threatened fishes of the world: Pangasius sanitwongsei Smith 1931 (Siluriformes: Pangasiidae)

Common name: Chao Phraya giant catfish (E), giant pangasius (E), pla thepa (Thai), pa leum (Lao), trey po pruy (Khmer). Conservation status: Endangered in Thailand (Humphrey and Bain 1990). Identification: Maximum size 300 cm TL, 300 kg. Long, dark filaments on anterior dorsal, pectoral, and pelvic rays (Rainboth 1996). Mouth width more than 17% SL (Roberts and Vidthayanon 1991). Distribution: Chao Phraya and Mekong River Basins in Southeast Asia. Abundance: The size and abundance of P. sanitwongsei has declined steadily over the past several decades. Smith (1945) reported fish up to 3 m from the Chao Phraya prior to 1920. By 1945, fish over 2 m were rare. By 1967, IUCN estimated fewer than 2,000 fish in the Chao Phraya (Humphrey and Bain 1990). P. sanitwongsei no longer occurs in the Chao Phraya River (Na-Nakorn et al. 2006). Along the Thai Mekong, fishermen report adult P. sanitwongsei disappeared around 1995. In Cambodia, fishers report a 60% decline since 1980 (Hogan et al. unpublished data). Habitat and ecology: Adults occur in deep pools areas. P. sanitwongsei is carnivorous, feeding on fish, shrimp, and crabs. Reproduction: Spawning occurs in April and May. Eggs adhesive, diameter of 2–2.5 mm, fecundity 433 600 eggs (41 kg female) and 876 800 (110 kg female). Broodstock show low genetic variation (NaNakorn et al. unpublished data). Threats: Overharvest, pollution, habitat fragmentation, and possible loss of forage base (Hogan et al. 2004). Lack of Environ Biol Fish (2009) 84:305–306 DOI 10.1007/s10641-008-9419-6