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The life history traits including growth, is the fundamental and key process of population dynamics and stock assessment, which gains much attention in recent years. Based on the data collected by Chinese observers onboard from 2013 to 2018, the growth of Bigeye tuna was analyzed, with the spatial-temporal variations. A total of 8,806 individuals were measured, with fork length ranging from 51 to 203 cm and the gilled & gutted & tailed weight from 2.5 to 138.0 kg. The predicted power length-weight function indicated that the estimate of condition factor a is 1.26 ×10-5 with spatial-temporal ranges 1.20~1.37×10-5, while the estimate of allometric growth parameter b is 3.05. Mixed effect models were established to estimate the variations from different years, quarters and regions, while 7 model candidates were considered with different random effects sources. AIC and Root Mean Square Error values revealed that the mixed effect model with all variations performed best. Results from the best model indicated that 1) there is no substantial different for Bigeye tuna in the north or south Indian Ocean divided by 15°S; 2) individuals collected in the quarter 1&2 tended to gain more weight than those collected in quarter 3&4 at the same length; and 3) individuals collected in 2015 and 2016 grew with better condition, while those in 2014 and 2017 gained much less weight at the same length. The outcome from this study could profit the stock assessment and fisheries management for this important tuna species in the Indian Ocean, and the methodology used in this paper can also be applied to the heterogeneity study for other species in both coast water and far ocean.
