Effects of Temperature and Dissolved Oxygen Levels on Hematological Responses of Juvenile Pacamã (Lophiosilurus alexandri)

Temperature and dissolved oxygen are key environmental factors influencing fish physiology, but their combined effects on the hematological profile of the Neotropical siluriform Lophiosilurus alexandri remain poorly understood. This study evaluated the isolated and interactive effects of temperature and dissolved oxygen on blood parameters of juvenile L. alexandri. Fish (mean weight 15.2 ± 2.1 g) were distributed in a completely randomized 2 × 2 factorial design, with two temperatures (28 and 34 °C) and two dissolved oxygen concentrations (2 and 5 mg L⁻¹), totaling four treatments with four replicates each (16 circular tanks of 28 L; stocking density: 1 fish per 2 L of water, resulting in 14 fish per tank). After 15 days of exposure under controlled water quality (pH 7.2–7.6, total ammonia < 0.3 mg L⁻¹), blood samples were collected for determination of hematocrit (%), hemoglobin (g dL⁻¹), erythrocyte count (× 10⁶ µL⁻¹), and derived indices: mean corpuscular volume (MCV, fL), mean corpuscular hemoglobin (MCH, pg), and mean corpuscular hemoglobin concentration (MCHC, g dL⁻¹). No significant effects of temperature, dissolved oxygen, or their interaction were detected for any of the hematological variables (two way ANOVA; P > 0.05 for all parameters). Hematological values remained stable across treatments, with hematocrit ranging from 17.8 to 19.0%, hemoglobin from 7.97 to 9.04 g dL⁻¹, and erythrocyte counts from 0.65 to 0.74 × 10⁶ µL⁻¹. These findings indicate that juvenile L. alexandri maintain hematological homeostasis when subjected to short term thermal and hypoxic challenges within the tested ranges, suggesting a degree of physiological tolerance to environmental fluctuations. This study provides baseline data on blood physiology for this species, contributing to the understanding of its adaptive capacity in aquaculture settings. Financial support: Dr. Bruno Bello Vicintin, in partnership with Rima Industrial S/A.