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The largehead hairtail, Trichiurus lepturus, is an opportunistic, voracious, and piscivorous predator. Studies of fish feeding behavior based on the analysis of stomach contents are limited by the potential for the visual identification of the ingesta. However, molecular tools, in particular DNA barcoding, have been used successfully to identify stomach contents. When morphological analyses are not possible, molecular tools can precisely identify the components of the diet of a fish based on its stomach contents. This study used mini barcoding to identify food items ingested by T. lepturus off the northern coast of São Paulo State, Brazil. Forty-six sequences were obtained and were diagnosed as belonging to six different fish species: Pimelodus maculatus, Paralonchurus brasiliensis, Isopisthus parvipinnis, Opisthonema oglinum, Harengula clupeola, and Pellona harroweri or as belonging to the genera Lycengraulis and Sardinella. Trichiurus lepturus is an opportunistic predator that will exploit an available prey of an appropriate size. The results indicate that these fish migrate to warmer waters, such as those found in estuarine environments, at certain times of the year, where they exploit prey species that reproduce in this environment. One example was Pimelodus maculatus, which was the prey species most exploited based on the analysis of the material collected. [ABSTRACT FROM AUTHOR]

Largehead hairtail (Trichiurus japonicus) in the China Seas shows an increasing catch trend, despite continued overexploitation, which could be attributed to improved recruitment as a result of strengthened early growth. To understand the early growth variability of largehead hairtail, we examined the linkages between early growth, as revealed by otolith microstructure, and the associated environmental variables over both spatial and temporal scales. Young‐of‐the‐Year largehead hairtail were collected from three regions in the Bohai, Yellow and East China Seas between 29° and 39° N. Daily increment widths of sagittal otoliths were measured and used as a proxy for somatic growth. We found two spawning cohorts, Spring‐ and Summer‐spawned cohorts, that showed latitudinal differences in both mean growth and growth pattern. The transition time from larval to juvenile stage was identified at around 40 days. Daily increment widths of two cohorts showed similar growth pattern in the first 40 days, while location had a marked effect on daily growth over 41–110 days. This suggests physiologically constrained growth pattern in larval stage, but more plastic growth subject to habitat‐specific influences in juvenile stage. The gradient forest analysis identified sea bottom temperature, vertical temperature gradient, and sea surface salinity, as the most important variables in determining early growth. Latitudinal differences in early growth pattern and their response to environmental variables suggest adaptive plasticity of early growth, which has notable implication for the management and sustainable utilization of this important but heavily exploited resource in the China Seas. [ABSTRACT FROM AUTHOR]

Fish is an important source of heavy metal exposition and contamination for human being. Accumulation of mercury (Hg) in men occurs by chronicle exposition, through the food chain, by ingestion of fish contaminated with mercury. Because of biomagnifications the carnivorous fish that is on the top of the food chain shows a higher concentration of mercury in their tissues and can represent the aquatic environmental contamination. This work aims to establish histopathologic analysis and total mercury concentration in different tissues from thirty-one Trichiurus lepturus, a commercial fish from Itaipu Beach, Niterói, RJ. T. lepturus collected showed mean values of total mercury concentration of 0.051±0.031μg g-1 and 0.006±0.004μg g-1, respectively in muscle and kidney tissues. It was also conducted an analysis of mercury concentration from a pool of brain tissue from all individuals (0.019μg g-1). Minimum and maximum mercury values in muscular and kidney tissues showed a wide dispersion. There was a positive correlation between total length and mercury muscular tissue concentration (R=0.85) and between body weight and mercury muscular tissue concentration (R=0.88), both highly significant. No significant correlation (r=0.24) was observed between kidney weight and mercury tissue concentration (P>0.19). In a multiple comparison test among muscle, kidneys and brain mercury tissue concentration, it was observed a highly significant difference between muscle and kidneys (P<0.001), as well as between muscle and brain (P<0.001). Comparison between kidney and brain mercury tissue concentration also showed a significant difference with a probability level of 5% (P<0.05). Histopathology demonstrated damage in the kidneys (cartilaginous metaplasia in some individuals and a high presence of melanomacrophage centers). [ABSTRACT FROM AUTHOR]