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Gila Chub Culture (Gila intermedia)

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September 2002 to December 2007

Scott Bonar

Andrew Shultz

Gila Chub Culture  (Gila intermedia)

The information needed to effectively culture imperiled native fishes for recovery efforts is lacking for certain species, yet is critical for proper management and conservation. Culture techniques and requirements are virtually unknown for Gila chub Gila intermedia, a species federally listed as endangered. We identified methods to spawn and rear Gila chub in captivity. Fish were brought to the laboratory in March 2003 from Sabino Creek, Arizona (12.3°C). Fish were then warmed slowly and spawned at 14.93°C, 10 d following collection. Following this initial spawning, Gila chub spawned consistently in the laboratory without hormonal, chemical, photoperiod, or drastic temperature manipulation, during all times of the year. Spawns were noted at temperatures ranging from about 15 to 26°C; however, we noted that Gila chub were more reluctant to spawn at temperatures above 24°C. Multiple spawning attempts per year per individual are likely. There was a strong, inverse relationship between time to hatch and incubation temperature. Hatch rate of eggs was high (mean = 99.43%) and larval Gila chub accepted a variety of natural and formulated diets at first feeding. We investigated the effect of different feed types on growth, survival, and overt health of larval and juvenile Gila chub. Larval Gila chub fed a commercial larval fish diet grew the same or slightly better than those fed thawed Artemia sp. nauplii, and significantly better than those fed chicken Gallus domesticus egg-yolk powder, but survived significantly better when fed Artemia. Despite the latter, observations suggest Artemia nauplii may be difficult for first-feeding larval Gila chub to handle. Thawed chironomid sp. larvae clearly outperformed prepared commercial feeds for small and large juvenile Gila chub with respect to growth; however, survival was 100% for all feed treatments. Overt health of larval and juvenile Gila chub remained largely unchanged during all experiments. Our results have shown first-feeding larval Gila chub may be reared on a natural or prepared diet but we recommend larval Gila chub be fed a natural feed if survival is paramount to objectives. Based on diets tested we recommend juvenile Gila chub be fed a natural diet if faster growth is paramount to objectives. Further work is suggested to define the nutritive requirements and identify the most efficient feeding regimen for Gila chub. We tested the effect of four different water temperatures on growth, survival, and overt health/appearance of larval (20, 24, 28, and 32°C) and two sizes of juvenile (20, 23, 26, and 29°C) Gila chub. Growth of larval Gila chub was highest at 28°C and lowest at 32°C, while survival of larval Gila chub was highest at 24°C and lowest at 20°C. Spinal deformities were common for larval Gila chub reared at 32°C but generally rare for those reared at lower temperatures. Although growth of small (32-49 mm TL) and large (52-72 mm TL) juvenile Gila chub increased with temperature, differences were not statistically significant. Survival was 100% (one accidental mortality) and no external abnormalities were noted in any experiment testing small and large juveniles. Water temperatures from 20-28°C appear suitable for rearing larval Gila chub, with temperatures from 24-28°C more optimal. Water temperatures from 20-29°C appear suitable for rearing juvenile Gila chub, with temperatures at the higher part of this range likely better for faster growth. We tested the effect of three different rearing densities on growth, survival, and overt health of larval Gila chub (0.065 g/L and 38.9 fish/L, 0.540 g/L and 319.5 fish/L, and 1.343 g/L and 795 fish/L), small juvenile Gila chub (3.618 g/L and 4.0 fish/L, 16.986 g/L and 20.1 fish/L, and 60.145 g/L and 68.3 fish/L), and large juvenile Gila chub (1.681 g/L and 0.4 fish/L, 14.346 g/L and 2.7 fish/L, and 53.942 g/L and 8.4 fish/L). Mean length and weight gain appeared inversely related to rearing density for larval and large juvenile Gila chub. Survival of larval Gila chub was significantly greater for those groups reared at low densities. Survival for juvenile Gila chub approached 100% for all density treatments. Few oddities in overt fish appearance/health were noted during the experiments and development for larval Gila chub largely followed growth rates. Our data strongly support increasing density having a negative effect on growth and survival (larval only) of Gila chub. These results are being presented in a Ph.D. thesis and publications. One publication on this work was published in the North American Journal of Aquaculture in January 2009.

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