Effects of surgically-implanted transmitters on survival and feeding behavior of adult English sole

Acoustic telemetry studies of flatfish have typically relied on an external transmitter attachment. We propose to initiate long-term monitoring of adult English sole (Pleuronectes vetulus Girard) movements in Puget Sound, Washington, USA. The transmitters we use have a 2-year battery life, and we are concerned that external attachment might result in increased tag loss or predation risk over the course of this study. Consequently, we conducted a laboratory study to assess the feasibility of surgically implanting the transmitters. Dummy transmitters were constructed with the exact dimensions and weight of the study transmitters (5 g in air, 9x30 mm) and coated with an epoxy resin. We collected adult English sole (>27 cm and 200 g) from Eagle Harbor, Washington, and tested insertion of a dummy transmitter into the peritoneal cavity from either the blind or eyed sides of the fish. A total of ten fish were assigned to each treatment group: blind-side insertion, eyed-side insertion and control. Two fish from each treatment were housed in each of five 1.2-m diameter tanks for 1 month. Fish were fed three times per week, and we noted their behavior for 10 minutes during each feeding. During the experiment, only one fish died (a control) and no transmitters were expelled. In addition, we found that fish from both treatments were active and exhibited normal feeding behavior relative to controls. At the conclusion of the experiment, all fish were weighed and sacrificed. Analysis of variance indicated no significant tank or treatment effects on weight gain. Necropsy revealed greater inflammation and fibrosis of the peritoneal side of the incisions made on the blind side relative to those on the eyed side. Therefore, we concluded that surgical implantation of transmitters into the peritoneal cavity is a viable option for long-term studies of flatfish movements, and we recommend insertion from the eyed-side of the fish.