Evaluation of the Viability and Growth of Walleye Embryos and Larvae after Antiviral Iodine Treatment

Abstract

AbstractAvoiding the transmission of viral disease and securing the health of fish populations are vital for hatchery‐based stocking programs in regions affected by viral hemorrhagic septicemia (VHS). Iodine compounds are nonselective antiviral substances that are widely used as disinfectants, but their effects on survival and growth during early life stages of fish require further study. Two groups of walleyes Sander vitreus were collected from the Maumee River (Perrysburg, Ohio) in March 2009. Group 1 (6 females and 3 males) was collected midmorning, and group 2 (10 females and 4 males) was collected that evening. Gametes were collected on site for group 1; group 2 fish were held in tanks overnight, and their gametes were collected the next morning. Gametes were transported (3–4 h) to the laboratory, where eggs from individual females were fertilized with the combined sperm of three to four males. Directly after fertilization and tannic acid treatment, embryos were exposed to iodine at 0 mg/L (control) or 100 mg/L (triplicate) for 30 min. Survival to the eyed embryo stage was estimated for both groups. Only larvae from group 1 were sampled prior to first feeding (live nauplii of brine shrimp Artemia spp.) at 9 d posthatch (dph) and approximately every 10 d thereafter until 48 dph to assess growth. Samples of eggs, ovarian fluid, larvae, and juveniles were collected for VHS testing. Survival to the eyed embryo stage for group 1 was not affected by treatment, but iodine treatment significantly decreased survival for group 2. Growth was unaffected by iodine treatment, and all samples that were tested for VHS were negative. Histological analysis of swim bladder morphology revealed that larvae with noninflated swim bladders had features of an undeveloped organ with hyperplastic epithelium consisting of vacuolarized cells. Walleye eggs that are collected according to the procedures used for group 1 can be treated with 100‐mg/L iodine for 30 min without sacrificing survival or growth in regions affected by VHS.