INFORMATIONAL ITEM            

 

 

Ecology of Larvae and Juveniles of Arroyo chub, Gila orcutti, a Native Southern California Coastal Fish Considered as a Potential Candidate for Mosquito Aquatic Biocontrol

 

  • Degradation of habitat and competition with exotic species have contributed to the depletion of the arroyo chub, Gila orcutti (California Species of Special Concern), a native southern California coastal freshwater fish being considered as a potential candidate for mosquitoes larvae biocontrol.

 

  • The arroyo chub, Gila orcutti, is more widely distributed, from Malibu Creek to San Luis Rey River, and much more widely distributed from introductions, from Chorro Creek in the north to the San Dieguito River drainage in the south. 

 

  • Habitat preferences: Juvenile and adult arroyo chub overlap with Santa Ana suckers in low-gradient stream habitats (0.5-2.5% slope) over sand, gravel, cobble, rock, and boulder substrates, but as gradient increases, chubs tend to be marginalized to lower-gradient sections or margins of steeper gradients and/or faster flows.

 

  • Chub freely invades standing backwaters and even ponds and reservoirs that are rarely occupied by other fish species. Adhesive eggs of arroyo chub attach to trailing vegetation or hard substrate in slowly flowing water, and larvae move into marginal standing or very slowly flowing water. As larvae grow and transform into juveniles, they invade faster-flowing water or can remain in standing water in absence of predators.

 

  • In areas with abundant exotic predators, such as the lower Santa Ana River within a few miles above Prado Dam, arroyo chub have been observed to be much rarer than Santa Ana sucker, or even absent. Apparently, their preference for a lower gradient makes them more vulnerable to predation by centrarchids and mosquitofish.

 

  • Further upstream of Prado Dam, arroyo chubs are common to abundant in 9 km of the river centered on the city of Riverside where gradient is higher and exotics less prevalent. An understanding of the larval ecology of native species may be crucial to the success of management efforts to enable these species to survive.

 

            R.F. Feeney and C.C. Swift, Ichtyol Res (2008) 55:65-77