Time-dependent post-mortem histomorphological changes in Penaeus vannamei following humane euthanasia

Histological analysis is a method commonly used in medical clinics to evaluate biological tissues and their abnormalities. However, this method is based on tissue collected from the necropsy of the animal, where modifications in the tissue associated with autolysis can occur after death. This study analyses the post-mortem histomorphological changes in white shrimp (Penaeus vannamei) after euthanasia by clove oil anaesthesia induction and pithing as a secondary killing method. The objective was to evaluate the natural progression of autolysis in specific tissues and determine the optimal time for collecting histopathological samples. Eighty clinically healthy juvenile shrimp were killed and analysed at 0, 10, 20, 40, 60, 120, 240, and 360 min post-mortem (mpd). Changes in colouration, muscle stiffness (rigor mortis), and tissue structure in the hepatopancreas, midgut, and antennal gland were examined. From 40 mpd onward, colour changes were observed in the musculature and hepatopancreas, accompanied by an increase in abdominal curvature due to the development of rigor mortis. The hepatopancreas exhibited the fastest rate of autolysis, followed by the midgut and antennal gland. Tissue integrity was lost at 10 mpd in the hepatopancreas and was severe from 60 mpd onward. A significant relationship was found between post-mortem time and the degree of tissue autolysis (r > 0.90, P < 0.001), with the hepatopancreas being the most severely affected tissue. The results indicate that post-mortem changes in P. vannamei occur rapidly, which can affect the interpretation of histopathological analyses if autolytic changes in tissues are not recognised as a post-mortem process. Immediate fixation of samples within the first 5 min after shrimp death is recommended to avoid significant alterations that could lead to misinterpretation in histological studies.