Histopathology of the Internal Anchor Tag in Spot and Spotted Seatrout

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Abstract
Pathological tissue changes elicited by an internal anchor tag in spot Leiostomus xanthurus and spotted seatrout Cynoscion nebulosus were evaluated histologcally. Forty-five spot (32 tagged fish and 13 untagged controls) and 13 tagged spotted seatrout were sampled periodically from 4 h to 4 months posttagging. Early tissue changes (4 h-4 d posttagging) in both species were characterized by acute inflammation and irritation. Changes included hemorrhage, fibrin exudation, extravasation of leukocytes, epidermal hyperplasia and spongiosis, and necrosis in exposed myotomes. Tags were progressively encapsulated and sequestered by fibrogranulation tissue in a similar sequence in both species, commencing with deposition and organization of fibrin at the tag surface. This early fibrinous capsule (at day 2) was infiltrated by leukocytes and fibroblasts, and by day 4-7 it was thickened, highly cellular, and well vascularized. Deposition of collagen within the granulation tissue capsule increased progressively for at least 8 weeks. Complications of this process occurred frequently in tagged spot, whereas the incision in control spot receiving no tag healed quickly and without complications. Almost all tagged spot showed secondary mycotic and bacterial infections, and several spot exhibited gross peritonitis. Other frequently observed complications included dislocation of scales, damage to peritoneum and ovaries by tag penetration, and displacement of tags with swimbladder or intestine. Several spot appeared actively to expel the internal anchor tag. Severe pathological changes in tagged spot suggest that both mortality and tag expulsion may have contributed to the relatively low (0.2%) tag return rate observed during the past 8 years for this sciaenid. We have discontinued tagging spot with the internal anchor tag and do not recommend its use. However, complications in spotted seatrout were minor, and tag expulsion was not observed. We have observed an 8.8% tag return rate and continue to tag this sciaenid with the internal anchor tag.

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