Changes in lysozyme concentrations over time in cultures of southern Bluefin Tuna, Thunnus maccoyii

Abstract

An 8-week trial in ranching cages was conducted to determine lysozyme concentration changes, and to examine the relationship between fish condition index, fish sizes, and fish lysozyme concentrations in southern bluefin tuna (SBT). Frozen pilchard were prepared for SBT each day during the ranching trial period. The results showed that lysozyme concentrations significantly increased in southern bluefin tuna over time in the culture. The lysozyme concentrations increased continuously from week 0 to week 8, from 26.09±13.46 to 215.91±62.11 µg/ml, representing an almost 800% increase. During the 8 weeks, the number of Cardicola forsteri and Caligus spp increased from 0 to 9.2±5.45 and 1.1±1.6, respectively. As C. forsteri or Caligus spp increased, lysozyme concentrations increased. In addition, the lysozyme concentration increased with increases in weight, length, and condition index. This study aimed to provide a theoretical basis for artificial SBT health cultures.