Studies on freshness of trawl catches. I. Freshness of fishes just after catching under various operating conditions of trawler in the tropical waters.

Abstract

Freshness of fish just after catching under various operating conditions by trawlers in the tropical waters was studied, taking opportunity of experimental trawlers by T/V Nagasaki-maru in the Andaman Sea in November 1981 and in the Gulf of Thailand in October 1982. The bottom water temperatures in the fishing grounds were about 28.5°C in both the seas.The mean K values of fish just after hauling up of the net were rather low; 5.6% for fish by one-hour of towing, 9.6% for fish by two-hours of towing, and 7.2% for fish by three-hours of towing. The mean K value for fish by one-hour of towing was significantly lower than those by two- and three-hours of towing, and this was also true for the same fish species caught in the same fishing ground. The distribution of K values was found to be exponential, the fish with K value of less than 10% accounting for 79.8% in one-hour of towing, 65.0% in two-hours of towing, and 80.0% in three-hours of towing.The mean K values of the fish caught in the Gulf of Thailand were significantly higher than those in the Andaman Sea. A higher occurrence of trash fish both in catch per hour and in percentage of total in the former area is considered to explain this partially.A negative correlation was found between the K values just after catching and the body weights of fishes, while between the K values and the increasing rates of K values we found a positive correlation.