A comparative study on antioxidant systems in semen of species of the Percidae, Salmonidae, Cyprinidae, and Lotidae for improving semen storage techniques

Abstract

The present study investigated the antioxidant systems in semen of different teleost fish species (burbot — Lota lota, perch — Perca fluviatilis, bleak — Alburnus alburnus, brown trout — Salmo trutta) with the intention to define types and effective concentrations of antioxidants suitable for supplementation of sperm storage solutions and cryopreservation extenders. Biochemical analysis revealed that in semen of L. lota, P. fluviatilis, A. alburnus, and S. trutta antioxidants (ascorbic acid, carnitine, glutathione, methionine, tocopherol, and uric acid) and oxidant defensive enzymes (catalase, gluthatione reductase, peroxidase, and superoxide dismutase) occurred in an almost similar qualitative and quantitative pattern whereby uric acid concentrations and superoxide dismutase activities were high while activities/concentrations of other enzymes and metabolites were low and/or fluctuating. Species-specific differences existed in the occurrence of catalase and carnitine. Important antioxidants and oxidant defensive enzymes were tested on their sperm protective effect in in vitro experiments. Spermatozoa were incubated in sperm motility-inhibiting saline solutions containing the antioxidants or enzymes and thereafter motility was activated with distilled water and measured and membrane integrity and sperm lipid peroxidation were determined. The experiments demonstrated that uric acid is the major antioxidant of semen of the investigated species, as it improves the sperm motility and membrane integrity and decreases the sperm lipid peroxidation. Therefore, supplementation of sperm diluents with uric acid can be recommended to increase the quality of semen whereby the effective concentration was 0.5 mmol/l for all investigated species. Also methionine has importance as antioxidant in teleost fish semen whereby the oxidized form (methionine sulfoxide) was most effective to increase sperm motility and membrane integrity. The effective concentration was 1.5–3 mmol/l. Finally, catalase improved sperm motility and membrane integrity in all species with exception of A. alburnus and therefore it can be useful to protect spermatozoa from reactive oxygen species, too. The optimal activity was 2 kU/l for P. fluviatilis and L. lota, and 0.1 kU/l for S. trutta.