DETECTING SWIM BLADDER INFLATION IN FINGERLING WALLEYES

The lack of swim bladder inflation has been recognized as a problem in intensively reared walleyes (Stizostedion vitreum) for many years. Th is phenomenon has also been recently observed in extensively reared wa lleye fingerlings. Four methods for detecting the presence of an infla ted swim bladder-light table, anesthesia, saltwater float, and radiogr aphic (X-ray)-were compared for accuracy, cost, and effect on survival . The light table method appeared to be fast and inexpensive, but was less accurate than the other three methods, probably because the fish were relatively large: the larger and more pigmented the fish, the mor e difficult the light table method is to use. The anesthesia method wa s accurate but time-consuming. The saltwater float method was accurate , simple, and cost-effective, but only dead fish were tested- The X-ra y method is easy, accurate, and provides a permanent record, but it is expensive. Survival was not affected by handling or anesthesia in the light table or anesthesia methods. Each method has certain advantages over the other methods; the method of choice would depend on the part icular situation (i.e., sorting versus quantifying).