Dietary spirulina and black cumin supplementation mitigate extreme warm temperature stress in Nile tilapia, Oreochromis niloticus

Global climate change has led to rising near-surface temperatures, posing major challenges for pond-based aquaculture systems where control of extreme heat is limited. The present study aimed to investigate whether Spirulina ( Spirulina platensis ) and black cumin ( Nigella sativa ) seeds in fish diets can mitigate extreme warm stress. Fish were fed either a control diet or diets supplemented with 1% Spirulina (SP 1%), 2% Spirulina (SP 2%), 0.75% black cumin seed (BC 0.75%), or 1% black cumin seed (BC 1%) for 35 days at 28 °C, followed by 15 days of exposure to extreme warm temperature (34 °C). Growth performance, hematobiochemical indices, intestinal histology, and ovarian development were evaluated. Fish fed Spirulina and black cumin supplemented diets exhibited significantly higher ( P < 0.05) final body weight, weight gain, and specific growth rate, along with reduced feed conversion ratio, at both temperatures. During warm exposure, supplemented groups showed significantly higher serum total protein ( P < 0.05) and lower levels of SGPT, triglycerides, and urea compared with the control. Hematological parameters, including RBC, WBC, hemoglobin, hematocrit, MCV, MCH, and MCHC, were better maintained in supplemented fish, whereas marked declines occurred in the control group at 34 °C. Intestinal histomorphology revealed significantly increased villus length, width, area, and goblet cell abundance in fish fed SP 2% and BC 1% diets. Ovarian development was also improved, with enhanced oocyte maturation and larger oocyte diameter in supplemented groups, while heat exposure induced ovarian deformities and increased immature oocytes in control fish. Overall, dietary Spirulina and black cumin seed supplementation effectively alleviated heat-induced stress and improved physiological resilience in Nile tilapia.