48 SEPTEMBER 2012 The western Pacific islands are the most important tuna fishing area in the world, accounting for one third of world tuna production (Gillett et al. 2001). Pelagic tuna, such as skipjack, yellowfin and other species, represents a substantial resource for the region (Allen and Bartram 2008). Landing, transshipment and processing of tuna from distant-water fishing fleets has become an important component of Guam’s economy (Fig. 1). In tuna processing, loins are retained and roe, along with other parts of the fish, are usually discarded. Roe accounts for about 16 percent of the tuna scraps and about 30 t of fish roe are wasted annually, as estimated by the manager of the largest tuna processing plant on Guam2. This processing waste is often sent to the local landfill. Tuna accumulate and preserve energy and essential nutrients in their roe for production of the next generation. Fish roe generally contains high levels of protein, cholesterol, phospholipids and highly unsaturated fatty acids. These essential nutrients are similar to those found in bloodworms and squid, which are commonly used as shrimp maturation diets. Using tuna roe in a shrimp maturation diet could reduce the organic dumping load and consequently alleviate environmental pollution. The effectiveness of tuna roe in boosting shrimp maturation, from health and nutritional perspectives, is unknown. A project funded by the USDA Center of Tropical and Subtropical Aquaculture was undertaken to develop techniques to increase the value of tuna roe by using it as an ingredient in a Litopenaeus vannamei maturation diet. In this project, we determined the nutritional value of tuna roe, confirm its pathogen-free status, developed a practical way to incorporate it into shrimp maturation diet, and evaluated its effectiveness as a suitable supplemental ingredient for shrimp maturation diet. Nutritional Value of Tuna Roe Raw tuna roe was processed by freeze drying, using a standardized procedure (30 gram sample freeze dry for 48 hours). The average dry matter of fish roe was 18.6 percent. Following freeze drying, six samples were shipped to the University of Hawaii for proximate nutrient analysis3 and fatty acid profiling4. Fish roe is abundant in protein (74.5 percent of dry matter). The values in Table 3 are baseline information for tuna roe, the major ingredient of the roe-based semi-moist diet. Samples were prepared by the method described in Tamaru et al. (1992) and fatty acid methyl esters were analyzed by gas chromatography. Total fatty acids account for 3.91 ± 0.71 percent (SD) of tuna roe dry matter. Previous studies on PUFA and HUFA profiles of natural foods for L. vannamei maturation suggested that supplementation of maturation diets with three HUFAs—arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—is needed (Lytle et al. 1990). Arachidonic acid is a precursor of prostaglandins, which play a role in controlling vitellogenesis. Shrimp oocyte EPA level is positively related to fecundity and DHA level is highly correlated with hatching rate, supporting their inclusion in shrimp maturation diets (Wouters et al. 2001). Bloodworms are generally considered to be the gold standard of shrimp maturation diets. Therefore, the fatty acid profile of tuna roe was compared to that of bloodworms (Lytle et al. 1990) to assess the suitability of fish roe as a shrimp maturation diet (Table 2). Among the total fatty acid fractions, ARA is 5 percent of total fatty acid fraction in tuna ovaries, which is slightly greater than that in bloodworms (4 percent). However, the EPA content of tuna roe (6 percent) was significantly less than that of bloodworm (29.3 percent). The DHA content of tuna roe is triple that of bloodworms. Consequently the EPA/DHA ratio is far lower in tuna roe (0.16) than in bloodworms (2.27), the latter of which is similar to that of shrimp ovarian tissue. Despite the large difference, the relationship between dietary EPA/DHA ratio and shrimp maturation remains unknown. Confirmation of SPF Status Using raw materials, such as bloodworm, presents a biosecurity concern because they can carry shrimp viruses that pose health risks to shrimp stocks. Shrimp disease outbreaks caused by viral agents remain the most profound threat to this fast growing industry sector and have caused billions of dollars in economic losses (Lightner 2005). Based on the severity of socioeconomic impacts of diseases caused by viruses, the World Animal Health Organization (OIE 2006) and USMSFP (2004) have listed the following pathogens to be excluded for specific-pathogen-free (SPF) shrimp stocks: IHHNV, YHV, TSV, IMNV and WSSV. Bloodworms have been passive vectors in the transmission of WSSV, the most deadly shrimp virus, to broodstocks (Vijayan et al. 2005, SupakLaoaroon et al. 2005) and subsequently to postlarvae (Withyachumnarnkul 1999). It is unclear whether other fresh-frozen maturation feeds serve as viral carriers. As a precaution, it is strongly recommended that fresh-frozen foods should be harvested from only low disease risk regions for use in maturation diets, such as squids from northern California and certified bloodworms from the United Kingdom. In addition, PCR screening should be implemented Using Yellowfin Tuna Roe in a Shrimp Maturation Diet Hui Gong 1 * and John W. Brown 1 Tuna roe is suitable for developing semi-moist shrimp maturation diets with proper texture and palatability.
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