Oxytetracycline Marking of Newly Hatched Walleye Fry

Abstract

Newly hatched walleye Sander vitreus (formerly Stizostedion vitreum) fry were treated by immersion in a solution of 700 mg of oxytetracycline hydrochloride (OTC)/L for 6 h to determine whether walleye fry could be marked at a younger age than previously described in the literature. The resulting marks varied in intensity but were observed on 100% of the fry inspected from groups that were treated at ages less than 24 h posthatch as well as those that were treated at ages less than 3 h posthatch. No false marks were observed on untreated controls in any of the treatment periods, and pond studies indicated no significant differences (P > 0.05) in either survival or growth between OTC‐treated fry and untreated controls. The results of this study demonstrate that walleye fry can be successfully marked immediately after hatching and that the entire annual production of walleye fry at a hatchery can be marked without additional fry‐holding facilities or significant disruption of routine hatchery operations.

Contribution and Performance of Stocked Walleyes in the Recovery of the Red Lakes, Minnesota, Fishery

“…Fry marking and stocking.-The eggs used to produce fry for rehabilitative stocking were obtained during the annual spawning run in the Pike River, Minnesota (a tributary to Lake Vermilion; Figure 1) and incubated at the Minnesota Department of Natural Resources (MNDNR) Fish Hatchery in Bemidji, Minnesota. The newly hatched fry (<24 h posthatch) were chemically marked prior to stocking by immersion for 6 h in a buffered solution of 700-mg active OTC/L (Logsdon et al 2004). The procedure used to mark the fry was similar to that first described by Brooks et al (1994) but with the maximum FDA allowable OTC concentration and immersion period (Fielder 2002;Lucchesi 2002;Logsdon et al 2004).…”

“…The newly hatched fry (<24 h posthatch) were chemically marked prior to stocking by immersion for 6 h in a buffered solution of 700-mg active OTC/L (Logsdon et al 2004). The procedure used to mark the fry was similar to that first described by Brooks et al (1994) but with the maximum FDA allowable OTC concentration and immersion period (Fielder 2002;Lucchesi 2002;Logsdon et al 2004). Treatments conducted prior to final FDA approval of the OTC immersion process in 2004 were authorized under Investigational New Animal Drug (INAD) exemption 9033.…”

“…Approximately 41 million Pike River fry were treated with OTC over a 10-d period in May 1999. A sample of 2,500 fry from the fourth day of treatment was transferred to a rearing pond at the MNDNR hatchery in Waterville, Minnesota, for mark efficacy evaluation (Logsdon et al 2004), and the remaining OTC-treated fry were stocked into the Red Lakes on the days that they were hatched. Approximately 32 million Pike River fry were also treated and stocked during 2001, and Additional OTC-treated fry that were hatched from eggs collected during the spawning run from the Red Lakes into the Blackduck River (Figure 1) were also stocked in 2004 and 2005 to help quantify natural reproduction after the Pike River Walleyes became sexually mature.…”

“…Prior to 1999, ages were assigned by RLDNR and MNDNR biologists based on inspection of either scales (Ambrose 1983) or broken otoliths (Heidinger and Clodfelter 1987). During the first 2 years that OTC-marked fish were expected to be present in the gill-net catches (2000 and 2001), however, both sagittal otoliths were reserved for OTC mark inspection and Walleyes were assigned to stocked or unstocked year-classes based on inspection of an unsectioned dorsal spine (Logsdon 2007 Oxytetracycline mark detection.-The remaining otoliths from the aging process were inspected for OTC marks using the methods described in Logsdon et al (2004). Comparison of mark observations with genetic stock identification during a previous study (Logsdon et al 2009) confirmed the persistence of the OTC marks but also indicated that mark assignment errors can result in somewhat fewer Walleyes identified as stocked (Pike River) fish than with the genetic techniques.…”

“…The identification of stocked fish has been particularly difficult for species such as Walleye Sander vitreus because they are commonly stocked as fry that are too small to allow conventional marking methods such as tags and fin clips (Brothers 1990;Younk and Cook 1991;Nielsen 1992). Immersion in oxytetracycline (OTC) hydrochloride has proved effective in producing long-lasting fluorescent marks on Walleye fry (Brooks et al 1994;Fielder 2002;Lucchesi 2002;Logsdon et al 2004Logsdon et al , 2009) and, after several years of successful marking trials (AADAP 2015), was approved in 2004 for use on food fish by the U.S. Food and Drug Administration (FDA 2015).…”