Dietary Shifts in the Adaptation to Changing Marine Resources: Insights from a Decadal Study on Greater Lizardfish (Saurida tumbil) in the Beibu Gulf, South China Sea

Understanding dietary behavior during the individual development of marine predators and its temporal variations elucidates how species adapt to changes in marine resources. This is crucial for predicting marine predators' habitat selection and the natural population's responses to environmental changes. The authors conducted a comparative analysis of dietary shift strategies and trophic level variations in Greater lizardfish (Saurida tumbil) in the Beibu Gulf during two distinct periods (2010 and 2020) using stomach content and stable isotope analysis methods. Possible driving factors for these changes were also explored. Changes in the fishery community structure and the decline in the abundance of primary prey resources have led the S. tumbil population to diversify their prey species, utilize alternative resources, and expand their foraging space. However, the species' foraging strategy, characterized by chasing and preying on schooling and pelagic prey, promoted stability in their feeding behavior across spatial and temporal scales. The main prey items remained demersal and pelagic fish species, followed by cephalopods and crustaceans. Similar to other generalist fish species, ontogenetic dietary shifts (ODSs) indicated a partial transition towards larger prey items. However, the timing and magnitude of the ODSs varied between the two periods, reflecting life-history variations and adaptive adjustments to environmental changes. In comparison to 2010, the population's mean body length (BL) increased in 2020, and the proportion of the population feeding on pelagic-neritic prey significantly increased. However, the δ15N values were lower, indicating that the shift in the ecological niche of preferred prey from demersal to pelagic-neritic was the primary cause of the decrease in trophic levels. In the future, we will conduct further quantitative research integrating the spatiotemporal data of both predators and prey to clarify the relationships between marine predators' feeding behavior, trophic levels, and changes in prey community structure.

Optimization of process conditions for effective ohmic heating of greater lizardfish () sausage via response surface methodology

In current research, the optimization of ohmic heating on greater lizardfish (Saurida tumbil) sausage variables was carried out using response surface methodology-central composite design (RSM-CCD). The effect of process variables including voltage gradient (15-60 V/cm), time (1-15 min), and temperature (60-90^°C) on the microbial properties, pH, peroxide value, water holding capacity (WHC), and cooking loss of the sausages was evaluated. The results showed that the characteristics of the sausages were dependent on the ohmic heating conditions and these properties can be modulated. As per the results, the voltage gradient and temperature has a significant effect on the total plate count (p < 0.05). The increase in voltage gradient was the most effective on pH (5.63-6.91). The interaction terms of all items had a significant effect (p < 0.05) on the peroxide value of the fish sausages. Higher amount of temperature and process time were resulted in the more cooking loss. Increasing the voltage gradient was more effective on WHC compared to the temperature. Finally, the process was optimized and the optimized condition was achieved by setting the voltage gradient at 30 V/cm, process time at 4 min, and temperature at 66°C. Also, it was compared with conventional heating. The results were shown that the differences between the mean values of all responses were statistically significant (p < 0.05) except for pH. Therefore, ohmic method was carried out faster, with lower temperature and obtaining the highest WHC and lowest total plate count, peroxide value, cooking loss, and optimized pH. Generally, this study suggested that the ohmic heating can be used as a rapid and homogeneous cooking method for the preparation of sausages from greater lizardfish as a commercial low-valued fish.

Stock differentiation of the greater lizardfish Saurida tumbil (Teleostei: Synodontidae) collected along the western coast of the Arabian Gulf and Sea of Oman using meristic characters

Meristic variation among stocks of greater lizardfish Saurida tumbil through the western coasts of the Arabian Gulf and Sea of Oman was examined using meristic characters. Statistical analysis of meristic traits proposed that there is constrained migration of populations of greater lizardfish along the western coast of the Arabian Gulf and Sea of Oman. Overlapping of the two samples from the northern part of the Arabian Gulf (Iraq-Kuwait waters), three samples from the middle region of the Arabian Gulf (Bahrain-Qatar-Saudi Arabia) and two samples from the southern part of the Arabian Gulf/Sea of Oman (United Arab Emirates-Sultanate of Oman) suggested that there are three self-recruiting populations in the studied area. Inspection of the role of each meristic trait variable to Canonical discriminant analysis showed that changes among samples appeared to be linked with the pattern of distribution of water temperature and configuration of current in both the Arabian Gulf and Sea of Oman areas.