Experimental Tuna Farming in the Sultanate of Oman

Abstract

Tuna are among a very large group of large and medium-oceanic fish and they are an important food source globally. They are also unusual fish because they are warm blooded fish and they need large amounts of oxygen. The fluctuations in tuna catch and price has led to focus on the farming of tuna in large floating cages in many countries, like South Australia, Turkey, Croatia, Mexico, Panama and other countries mainly for the Japanese market. In the Mediterranean they farm blue fin tuna, yellow fin tuna and big-eye are farmed in Mexico and the yellow fin tuna have been farmed on a pilot scale in the Sultanate of Oman by cage Culture Company. To farm tuna several stages have to be practiced, starting from preparation of cages, fishing, transferring of the live fish to the towing cages and to the farming site, feeding, harvesting, processing, packaging and exportation. In Oman, two types of cages were used in this process, towing cages and fattening cages, and with nets of 30meters depth, fixed on cages of 48meters diameter. Fishing was practiced using Purse-Seineships in areas around 50-70 kilometers away from the farming sites, nets were kept open to avoid killing of fish, which transferred under water to the towing cages then to the fattening cages. The speed of ship didn’t exceed 4 nots/hour through the whole journey. Tuna arrives to the farming site in a state of stress and seize eating for up to 3 weeks even if an attempt is made to feed them. After this period, tuna start feeding greedily large quantities of food with high oils content such as Sardine. When caught fish weight ranges from 25-40 KG, and there is no need to gain more weight but to increase the percentage of fat. In the Sultanate we used sardines, as the Omani sardine is characterized by high oil content. Feeding was distributed manually to the cage until the tuna stop eating. The fish lose about 20% of its weight during transportation and fasting stage, then compensate the loss and increase the percentage of oil in the flesh. Generally the universal calculated food conversion ratio is 1-20 as the fresh fish used in feeding has high proportion of water. Harvesting process is a delicate process and should be organized well and requires accuracy and speed at work, relies on the use special collection net to collects almost the required number and detain it in the cage. Professional divers have to dive and swim with a hold of fish. The caught tuna then lifted from the waterslide on the smooth floating portion to reduce friction with the fish’s body. Followed by quick killing of fish by putting steel nail in the brains of the fish to reduce stress and avoid burning of the meat. The second step is the insert of steel wire in the spinal cord after cutting the head using an electrics a win order to ensure the full death of the fish. Fish are then placed in ice water to ensure cooling of the meat and quality; the last stage is to transfer the fish to the factory for processing and exportation. Normally harvesting should not take more than 2-3 minutes to keep the meet to the highest quality or Shesimi grade for the Japanese market. Dealing with farmed tuna inside the processing plant should be in a way that maintains fish quality and maintain me at temperature internally and externally and determine the quality of meat in terms of the percentage of the fats in fish flesh.