Identification of freeze-thaw artifact in fresh and decomposed black rockfish (Sebastes melanops) and steelhead trout (Oncorhynchus mykiss). Issue 6 (November 2022)

• Record Type: Journal Article
• Authors: Kagan, Rebecca; Viner, Tabitha C.
• Is Part Of: Veterinary pathology. Volume 59:Issue 6(2022)
• Page Start: 1022
• Page End: 1030
• Publication Date: 2022-11
• Subjects: fish -- forensic pathology -- freeze artifact -- histopathology -- skeletal muscle -- wildlife; Veterinary pathology -- Periodicals; Pathology, Veterinary -- Periodicals; 636.089607
• DOI: 10.1177/03009858221120012
• Languages: English
• ISSNs: 0300-9858

Abstract

Identification of freeze-thaw artifact in fish can help to determine whether they have been harvested within the appropriate season and monitor adherence to fishing regulations. Recognition of freeze-specific changes will also prevent potential misinterpretation due to decomposition, disease, injury, or species variation. An initial survey using black rockfish ( Sebastes melanops ) identified which tissues reliably exhibit freeze artifact. Tissues were exposed to different treatments: immediate formalin fixation; refrigeration or storage at room temperature for 24, 48, or 72 hours; or freezing for 1, 8, or 28 days. Three fish underwent a combination of treatments. Tissue changes in each treatment group were compared macroscopically and microscopically. Macroscopic changes in frozen-thawed and never-frozen fish overlapped somewhat; however, microscopic findings of skeletal myocyte cavitation, lens liquefaction, and brain tissue fractures were consistent findings only in frozen-thawed tissues. A validation study was then done to establish the accuracy of microscopic analysis. Brain and paired ocular and skeletal muscle samples from 61 steelhead trout ( Oncorhynchus mykiss ) were fixed in formalin either fresh or after being frozen for 4 weeks. Weighted kappa values showed both high observer accuracy and interobserver agreement in the identification of freeze-thaw status. Based on these findings, microscopic changes in the skeletal muscle, eye, and brain are considered consistent and easily identifiable indicators of a previous freeze-thaw cycle and should not be confused with a pathologic process.