Metabolism of intratesticular spermatozoa of a tropical teleost fish ( Clarias gariepinus)

Abstract

Sperm metabolism of a tropical fish species, the African catfish, Clarias gariepinus, was studied by measurements of sperm enzyme activity and metabolite levels. We also analysed the effect of metabolites, co-enzymes and enzymatic blockers on sperm motility behaviour and viability. Similar to other teleostean species, African catfish spermatozoa have the capacity for glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, lipid catabolism, β-oxidation and osmoregulation. In immotile spermatozoa, lipid catabolism, β-oxidation, the tricarboxylic acid cycle and oxidative phosphorylation were important primary energy-delivering pathways; sperm oxygen consumption was 0.39–0.85 μg O 2/min/ ml of testicular semen. During motility, glycolysis, lipid catabolism and β-oxidation of fatty acids occurred simultaneously, which is atypical for teleosts, and the spermatozoal respiration rate increased drastically by 15–25-fold. Also in contrast to other teleostean sperm cells, ATP levels remained stable during motility and immotile storage. The sperm cell status was unstable in the African catfish. Although the spermatozoa have osmoregulation ability, and even though balanced physiological saline solutions were used for sperm motility activation and sperm incubation, the motility and viability of spermatozoa quickly decreased at 28 °C, the spawning temperature of the African catfish. Cyclic AMP and inhibition of phosphodiesterase activity could not prolong sperm motility and viability. In contrast, at 6–10 °C motility was prolonged from approximately 30 s to >5 min, probably due to decreased metabolic rates.