Mechanisms of Digestive Enzyme Response to Acute Salinity Stress in Juvenile Yellowfin Tuna (Thunnus albacares).

This study investigates the effect of a sudden change in salinity for 48 h on the digestive enzyme activity of juvenile yellowfin tuna. The treatment included a control salinity of 32‱ in natural seawater and an experimental salinity of 29‱. Acute stress experiments were carried out on 72 juvenile yellowfin tuna (646.52 ± 66.32 g) for 48 h to determine changes in digestive enzyme activity in different intestinal sections over time (0 h, 12 h, 24 h, 48 h). The activities of pepsin, trypsin, α-amylase, lipase, and chymotrypsin in the digestive organs (stomach, foregut, and pyloric ceca) of juvenile yellowfin tuna were measured. Pepsin and pancreatic protease in the experimental group were significantly lower than in the control group (p < 0.05). α-amylase showed a fluctuating trend of decreasing and then increasing, and its activity trend was pyloric ceca > foregut > stomach. The lipase activity of gastric tissues decreased at the beginning and then increased, reaching a minimum at 24 h (2.74 ± 1.99 U·g protein-1). The change of lipase in the pyloric ceca and foregut was increasing and then decreasing. The lipase activity trend was pyloric ceca > foregut > stomach. The chymotrypsin showed a decreasing and increasing trend and then stabilized at 48 h with a pattern of pyloric ceca > foregut > stomach. Similarly, the gut villi morphology was not significantly altered in the acutely salinity-stressed compared to the non-salinity-stressed. This study suggests that salinity may change the digestive function of juvenile yellowfin tuna, thereby affecting fish feeding, growth, and development. On the contrary, yellowfin tuna is highly adapted to 29‱ salinity. However, excessive stress may negatively affect digestive enzyme activity and reduce fish digestibility. This study may provide a scientific basis for a coastal aquaculture water environment for yellowfin tuna farming, which may guide the development and cultivation of aquaculture.

Preparation of a Novel Straw-Sludge Activated Biochar and Its Adsorption Mechanisms for Removal of VOCs.

To simultaneously achieve the objectives of waste resource utilization and clean production, a novel approach involving the utilization of corn straw-sludge hybrid biochar was proposed for the adsorption of VOCs emitted from biomass power plants. This study analyzed the effect of straw-sludge biochar on the adsorption characteristics of VOCs (toluene, isopentane, and ethylene) under different preparation conditions (raw material ratio, activation temperature, and activation time). The findings revealed that the adsorption efficiency of the mixed biochar was significantly superior to that of individual corn straw biochar and sludge biochar. The adsorption of methylbenzene, isopentane, and ethylene was 78.32, 40.81, and 41.18% higher, respectively, compared to the control groups consisting of pure sludge biochar and pure corn straw biochar. Moreover, the adsorption performance of the activated biochar followed the sequence of ethylene < isopentane < methylbenzene in terms of both saturation time and adsorption capacity. The adsorption capacity of VOCs on straw biochar-sludge biochar demonstrated a consistent correlation with the boiling point and molecular weight of the adsorbate, with higher adsorption capacities observed for adsorbates with larger boiling points and molecular weights, specifically methylbenzene > isopentane > ethylene.