Seasonal Environmental Variability Drives Physiological Adaptations in the Thick-Lipped Grey Mullet (Chelon labrosus) of the Southern Mediterranean Sea

Abstract

Abstract: This study investigated the impact of seasonal variations in temperature, salinity, and dissolved oxygen in Ras Al-Tin lagoon (Eastern Libya) on hematological, liver, and kidney functions of Chelon labrosus. Surface water parameters ranged as follows: temperature (11-23°C), salinity (4.67-23%), conductivity (11-27 mS/cm), and dissolved oxygen (9.5-11.9 mg/1). Blood samples from 40 fish collected seasonally in 2019 revealed significant physiological changes. Hematological results showed peak WBCs (185.32 ± 18.27 x 103/ul) and RBCs (2.75 ± 0.25 x 10/μl) in autumn, while summer exhibited the lowest HGB (5.86 ±1.56 g/dl) and HCT (19.96 ± 6.04%). MCV and MCH peaked in spring (171.10 ± 4.80 fl; 61.15 ± 1.15 pg), whereas MCHC was highest in winter (36.04 ± 1.57 g/dl). Liver enzymes GOT and GPT spiked in autumn (229.75 ± 40.33 U/L; 23.25 ± 2.66 U/L), while LDH surged in spring (1331.00 +86.00 U/L). Kidney function markers urea and creatinine peaked in spring (39.00 ± 5.00 mg/dl; 0.75 ± 0.05 mg/dl), whereas uric acid was elevated in autumn and summer. These findings suggest that moderate temperatures in spring and autumn correlate with heightened metabolic and reproductive activity, supported by increased enzyme levels and hematological shifts. Seasonal extremes (summer/winter) likely induced stress, reflected in reduced