Sensitivity of Guadalupe Bass Swim‐up Fry to Hyperoxia

Abstract

Hatchery-reared fingerling Guadalupe Bass Micropterus treculii are stocked into central Texas rivers to restore threatened populations and combat hybridization with Smallmouth Bass M. dolomieu. Fry survival in hatchery rearing ponds has declined by more than 50% in recent years, and pilot investigations indicated that exposure to high dissolved oxygen (DO) concentrations (>20 mg/L; hyperoxia) during tempering might have contributed to fry mortality. To test this hypothesis, Guadalupe Bass swim-up fry (11 d posthatch; 8.45 ± 0.25 mm TL [mean ± SD]) were exposed to normbaric DO concentrations ranging from 7.9 to 33.3 mg/L at 18°C, mimicking the hatchery tempering protocols followed during 2014 and 2015. After a 30-min exposure to the DO treatment (flow rate = 18 L/ h), jars were flushed with nonoxygenated water for 1 min to rapidly lower the DO, mimicking the release of fry into ponds after tempering. Jars were then supplied with freshwater at a rate of 36 L/h and were monitored for 72 h. One control (A) was subjected to the same protocol but without oxygen supplementation; the other control (B) was not subjected to the 30-min exposure or flushing. Dead fry among treatments were recorded and removed every 24 h. Mortalities were observed within 6 h. Surviving fry were counted and measured after 72 h. Fry survival at 72 h was negatively correlated with increasing DO concentrations (Pearson's product-moment correlation coefficient = -0.79) and declined significantly above 20 mg/L. Fry populations exposed to the highest oxygen concentration visually appeared more lethargic than fry in other treatments. The results of our study suggest that hyperoxia contributed to the low survival of fry in recent years. We recommend DO concentrations below 15 mg/L and avoiding DO levels above 20 mg/L (212% saturation at 18°C) when transporting and tempering Guadalupe Bass fry. We also recommend verifying the oxygen limits of other black bass Micropterus spp.

The Early Life History of the Guadalupe Bass: Lessons for Culturing a Threatened Species

“…() suggested that GB fry are sensitive to hypo‐ and hyperoxia soon after swim‐up, so DO must be maintained between 6 and 15 mg/L during acclimation (Matthews et al. ). Maintaining DO within this range throughout GB larval culture would be prudent.…”

“…Some aspects of GB early life history (spawning season and location, fecundity, some nest and egg characteristics, and behavior) have been partially described by Hurst et al (1975), Boyer et al (1977), Edwards (1980), and Carmichael and Williamson (1986). Other published observations on GB have primarily focused on water quality tolerance (Edwards 1978(Edwards , 1980Tomasso and Carmichael 1986;Sullivan et al 2013;Matthews et al 2017), introgression with SMB (Edwards 1979(Edwards , 1980Whitmore and Butler 1982;Whitmore 1983;Garrett 1988Garrett , 1991Morizot et al 1991;Littrell et al 2007;Bean et al 2013;Bean and Grabowski 2015;Fleming et al 2015), habitat (Hubbs 1957;Edwards 1978Edwards , 1980Farquhar 1995;Perkin et al 2010;Bean and Grabowski 2015), phylogeny (Johnson et al 2001;Bagley et al 2011), and reproductive behavior (Lutz-Carrillo et al 2015). Studies of the GB diet are limited to observations of predominantly juvenile and adult fish (Edwards 1980;Day 1981;Carmichael and Williamson 1986;Farquhar 1995).…”

“…; Matthews et al. ), introgression with SMB (Edwards , ; Whitmore and Butler ; Whitmore ; Garrett , ; Morizot et al. ; Littrell et al.…”

“…The variable survival of GB fingerlings in ponds at the A. E. Wood State Fish Hatchery (AEW) has made efficiently meeting the annual fingerling request challenging (Matthews et al. ). Blaxter () reported that potential critical periods of high mortality during fish development include first feeding (the shift from endogenous to exogenous food sources), the shift in dominant respiration from cutaneous to gill, and swim‐up (first filling of the swim bladder).…”

“…PRANGNELL AND MATTHEWS cutaneous to branchial respiration is accelerating (Blaxter 1988). Matthews et al (2017) suggested that GB fry are sensitive to hypo-and hyperoxia soon after swim-up, so DO must be maintained between 6 and 15 mg/L during acclimation (Matthews et al 2017). Maintaining DO within this range throughout GB larval culture would be prudent.…”