Effects of dietary sodium alginate on growth, immune, antioxidant biomarkers, histological structure, and hyperthermia stress tolerance of thin-lip grey mullet (Liza ramada) fingerlings

The primary goal of this experiment was to explore the consequences of dietary supplementation of sodium alginate (SA) at levels of 0.0 % (SA0), 1 % (SA1), 2 % (SA2), and 3 % (SA3) on growth performance, immune and antioxidative biomarkers, and internal organs (liver, gills, and intestine) architecture of thin-lip grey mullet (Liza ramada) fingerlings. Fish (6.25 ± 0.20 g) were fed on the experimental diets up to apparent satiety thrice a day for 10 weeks. After that, hyperthermia stress tolerance was investigated via sudden exposure of fish to 32 °C where their mortality rate and the time of death were recorded throughout 4 h. The findings herein showed that feeding L. ramada with 2 % SA significantly exhibited the best fish growth and feed utility. However, no significant alterations were registered in the carcass chemical composition among different fish groups. Compared with other SA groups, the high level of SA (3 %) induced highest levels of glucose, urea, creatinine, aspartate aminotransferase, and alanine transaminase. The immune and antioxidant biomarkers in the SA2 group (2 % SA) displayed noticeably higher levels compared with other SA-fed fish groups. The histological examination of liver, gills, and intestine tissues of L. ramada fingerlings fed on SA0, SA1, and SA2 diets showed normal histological structure but slight alterations were observed with SA3 group. After the hyperthermia stress test, it is noted that the control group (SA0) started to die at 13 – 44 min and needed 115–132 min to die completely. On the 0ther hand, feeding thin-lip mullet fingerlings on SA diets; particularly 2 % SA, showed higher survivability and needed more time to die completely (>180 min). In conclusion, using 2 % SA as a feed supplement in diets for L. ramada induced better performance, immune and antioxidant capacity, and enhanced their tolerance against possible hyperthermia stress.