Temperature Modulation of Growth and Physiology of Juvenile Guadalupe Bass

Fingerling Guadalupe Bass Micropterus treculii were cultured in 18, 21, 24, 27, or 30◦C water for 6 weeks. Temperature affected the growth of the Guadalupe Bass when it was measured by increases in TL but not when measured by increase in mass. The optimal temperature for growth of Guadalupe Bass was 27–28◦C. Condition factor increased linearly with temperature, indicating that the fish were plumper at warmer temperatures. The mean hematocrit was 37 and not significantly affected by temperature, although a trend of increasing hematocrit with increasing temperature was apparent. The liver index varied significantly with temperature, and the maximum index was at 24◦C. The results of this study provide basic thermal information and some base line hematological values for hatchery production and management of Guadalupe Bass. The Guadalupe Bass Micropterus treculii is a streamdwelling black bass native to the Edwards Plateau region of southcentral Texas. It is a species of special concern in Texas due to limited natural distribution and genetic introgression with introduced black bass, particularly the Smallmouth Bass Micropterus dolomieu (Whitmore 1983; Warren et al. 2000; Littrell et al. 2007; Bonner and Bean 2008). The stocking of hatcheryproduced Guadalupe Bass fingerlings is a part of the recovery effort for this species. Beyond some information on spawning and hatching conditions (Carmichael and Williamson 1986) and toxicity of nitrogenous wastes (Tomasso and Carmichael 1986), little is known of the environmental requirements of Guadalupe Bass. To develop a broader base of environmental information for hatchery managers, this study determined the effects of temperature on growth and body condition of Guadalupe Bass. We also observed the effect of rearing temperature on hematocrit, liver index, and body condition, which are indicators of general fish health (Barton et al. 2002). *Corresponding author: [email protected] Received September 24, 2012; accepted March 9, 2013 METHODS Approximately 400 Guadalupe Bass fingerlings (59–108 mm TL) were obtained from the A.E. Wood Fish Hatchery (Texas Parks and Wildlife Department) in May 2011. The fish were trained to consume prepared feed by generally following Carmichael and Williamson (1986). Briefly, fish were held in indoor fiberglass tanks receiving constantly flowing spring water (22◦C). Initially, fish were offered a mixture of dried, crushed krill and silverside and a prepared pellet (BioDiet Grower C ©; Bio-Oregon, Longview, Washington: 43% protein, 14% oil, 1% fiber). During training, feed was offered at least 10 times/d, and the proportion of prepared pellet was increased as fish began to feed consistently. During training, approximately 5% of the fish died. Fish were transferred to experimental systems after they had been readily taking prepared pellets for at least 2 weeks. Thirty individuals were stocked into each of six 300-L water recirculating systems (Living Streams, Frigid Units, Toledo, Ohio), and then water temperatures were adjusted at a rate of approximately ±0.5◦C per day (starting water temperature was approximately 22◦C) until temperatures in Living Streams were nominal 18, 21, 24 (two Living Streams), 27, or 30◦C with a thermostat resolution of ±1.0◦C. After all Living Streams reached their nominal temperatures, fish in each were anesthetized with tricaine methanesulfonate at 2 g/L of water, weighed individually, and returned to the Living Stream from which they were collected. Averaged fish weight was 4.7 g (SD, 1.47). Mean fish weight varied significantly (analysis of variance [ANOVA]; P < 0.001) among Living Streams; means ranged from 3.9 to 5.3 g, being higher in the warmer tanks, which was due to thermally controlled differential growth during the acclimation period. After weighing, fish were exposed to experimental temperatures for 6 weeks and were fed to satiation once per day. During the 373 D ow nl oa de d by [ T ex as S ta te U ni ve rs ity S an M ar co s] a t 1 4: 10 1 7 M ay 2 01 3