Effects of Dietary Supplementation of Natural Spirulina on Growth Performance, Hemato-Biochemical Indices, Gut Health, and Disease Resistance to Aeromonas Hydrophila of Stinging Catfish (heteropneustes Fossilis) Fingerling

Spirulina is a popular edible blue-green alga that has piqued the interest of aqua-feed formulations due to its high concentration of micronutrients, macronutrients, and antioxidants. To investigate the impacts of natural Spirulina as a feed additive on Stinging catfish (Heteropneustes fossilis) growth, feed utilization, hematology and serum biochemistry, gut morphology, as well as disease resistance to Aeromonas hydrophila, a 60-day feeding experiment was performed. The fish (N = 240), with an initial weight of 4.23 +/- 0.50 g, were placed in 12 aquaria tanks (100 L/ tank) and fed twice daily until they were satisfied. Four different experimental diets: 0% (D0, control diet), 1% (D1), 3% (D2), and 5% (D3) natural Spirulina meal were used to feed the fish. This study found that Stinging catfish fed with a 5% Spirulina diet obtained notably higher (p < 0.05) specific growth rate, final weight, weight gain, and average daily weight gain than other supplemented regimens. Furthermore, as Spirulina inclusion in diets increased, feed utilization parameters such as feed conversion ratio and protein efficiency ratio improved remarkably (p < 0.05). Red blood cell, white blood cell, lymphocytes, neutrophil, monocytes, basophil, hemoglobin, red cell distribution width-standard deviation, and mean corpuscular hemoglobin were all substantially (p < 0.05) greater in 5% Spirulina diet-fed fish. The basal diet-fed fish had lower (p < 0.05) total protein, globulin, and albumin levels and higher glucose, cholesterol, and triglyceride levels than those fed with other test diets. Compared to other fish groups, light microscopic examination of intestinal tissues revealed that fish fed 3% and 5% Spirulina had well-organized enterocytes, intact epithelial barrier, abundant goblet cells, and lacking luminal cell debris, as well as exhibited no signs of inflammation (edema). Spirulina diets significantly (p < 0.05) affected intestinal villi height and width, mucosa width, crypt depth, villi, and lumen area. Furthermore, a 5% Spirulina diet-fed fish demonstrated remarkably (p < 0.05) greater resistance (68.57%) to A. hydrophila during the bacterial challenge trial. Based on the findings, applying natural Spirulina powder at 5% in diets as a feed supplement could benefit H. fossilis nutrient utilization, growth performance, health status, as well as disease resistance.