Application of sodium alginate solution for short-term storage of different volumes of sex-reversed rainbow trout (Oncorhynchus mykiss) testicular sperm

Abstract

The effect of 0.8% sodium alginate (alginate) addition to Morisawa solution (MS) at pH 8.5 containing 100 mM NaCl, 40 mM KCl, 3 mM CaCl2, 1.5 mM MgCl2 and 50 mM Tris supplemented with an antibiotic (10,000 units penicillin and 10 mg streptomycin per mL in 0.9%) on sex-reversed rainbow trout (Oncorhynchus mykiss) short-term sperm storage for 12 days under anaerobic conditions (4 °C) was tested. Sex-reversed rainbow trout sperm, i.e., testicular sperm (TS), was diluted tenfold in MS + alginate (1:9; TS:MS + alginate) and short-term stored in different containers: an microtube (Mt) with 500 μl capacity, a glass container (Gc) with a 25 ml capacity and a plastic container (Pc) with a 120 ml capacity. In each storage container, TS was short-term stored in sperm columns at two different heights, 0.5 cm (sperm storage volume: 180 μl, 4 ml and 9 ml for Mt., Gc and Pc, respectively) and 1.0 cm (sperm storage volume: 200 μl, 8 ml and 18 ml for Mt., Gc and Pc, respectively). As a control, TS diluted in MS without alginate addition was applied, and sperm were stored for a short time under the same conditions, i.e., storage time, dilution ratio, containers and sperm column height. During the experiment, sperm motility (MOT, %) and sperm curvilinear velocity (VCL, μm s−1) were analyzed at 0, 4, 8 and 12 days during TS short-term storage. It was found that the efficiency of short-term storage of sex-reversed rainbow trout TS was determined both by the sperm column height used (stored sperm volume) and by the addition of MS supplements limiting sperm sedimentation during storage, i.e., 0.8% sodium alginate. Over 12 days, the best storage effects (based on CASA parameters) were obtained when TS was short-term stored in Pc using a 9 ml sperm volume, regardless of alginate addition to MS. In contrast, in Mt. (180 and 200 μl sperm storage volume), TS lost its ability to move more quickly, i.e., on the 4th day, mainly in short-term trials without the addition of alginate. The results also indicate that incorporation of alginate into MS significantly reduces TS sedimentation and enhances fertilization capacity during short-term storage over 12 days, especially at a 1.0 cm sperm column height, i.e., using 200 μl, 8 ml and 18 ml sperm volumes for short-term storage in Mt., Gc and Pc, respectively.