PREDICTION OF SOMATIC GROWTH PATTERN FROM CHANGES IN RNA, DNA AND PROTEIN SYNTHESIS AT EARLY STAGES IN YELLOWFIN TUNA, Thunnus albacares  

Yellowfin tuna (YFT) demand has been increased worldwide because of its multipurpose usage as raw and processed fish. To meet its demand, fishermen have been captured from the nature to supply in the market, which has been affected the stock as well as the eco-system. Therefore, it is important to establish a sustainable culture system for this species. However, it is important to know the somatic growth pattern at early larval and juvenile stages in order to predict their feeding behavior as well as to formulate artificial feed and establish mass seedling production, which are prerequisite for sustainable aquaculture. Therefore, RNA, DNA, and protein content were assessed to evaluate somatic growth in larval and juvenile YFT.

Experimental fish were reared at the Inter-American Tropical Tuna Commission's Achotines Laboratory in Los Santos, Panama. During rearing period, fish were fed with rotifer, Artemia and newly hatched yolk-sac larvae of YFT, and sampled at 1, 3, 4, 6, 9, 12, 15, 17, 22, 27, and 33 day after hatch (DAH) for length, weight, RNA, DNA and protein determination.

Standard length and dry body weight rapidly increased from 15~17 DAH (flexion-postflexion phase). The RNA-DNA ratio rapidly increased between 17~22 DAH (postflexion phase), suggesting that protein synthesis increased at some point here in order to induce organ and tissue differentiation. The protein-DNA ratio, which is an indicator of cell volume, also rapidly increased between 17~22 DAH (postflexion phase), indicating an increase in cell volume. This is also supported by increase in condition factor at this stage. The higher ratio of both protein-DNA and RNA-DNA between 22~33 DAH suggests that the observed growth in the early juvenile phase was due to both increasing cell number and volume. The rapid growth due to the increase in both cell number and volume at the early juvenile stage also urges feed supply with proper nutritional balance to ensure mass seedling production.