Considering Two Aspects of Fish Welfare on African Catfish (Clarias gariepinus) Fillet throughout Postmortem Condition: Efficiency and Mechanisms

Knowledge about fish welfare and its impact on fish fillet quality is still insufficient. Therefore, the influence of two aspects of fish welfare (slaughtering method: bled and unbled fish; fish stock densities: 90, 120, and 150 kg·m(−3)) on African catfish fillet quality during postmortem conditions was investigated. The aim of study was to determine (i) the efficiency of bleeding on oxidation progress and (ii) the influence of stock density on fillet quality. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE) showed a higher protein loss in the unbled than in the bled groups, especially in the heavy myosin chain (MHC) band. However, density did not show any influence on protein profile. Western blot analysis showed fewer oxidized carbonyls in the bled than in the unbled groups; higher oxidation development, microbial growth, and lower hardness were observed in unbled fillets. Additionally, hardness was higher at 90 and 120 kg·m(−3) densities in bled fillet compared to 150 kg·m(−3). The first three days of storage showed a higher oxidation rate in unbled fillets than in bled fillets, confirming the contribution of hemoglobin to oxidation development with different mechanisms of protein oxidation. The obtained results revealed the same fillet quality in all aspects at either 90 or 120 (kg·m(−3)) stock densities, which would suggest 120 kg·m(−3) for the fishery industry. However, higher stocking density in this study would not be appropriate for fish welfare.