Table 2.

Fertility evaluation (in Trial 2) of cryopreserved sperm of medaka Oryzias latipes by using methanol (10%) as cryoprotectant combined with a cooling rate of 10 °C/min from 5°C to -80 °C. The characteristics reported are standard length (cm), body weight (g), and testis weight (mg), motility before freezing and after thawing, and fertility of cryopreserved sperm including fertilization (percentage of eggs developed to blastula stage) and hatching (percentage of hatched fry in relation to total number of eggs) of the 20 individual males used. Quality of the eggs was evaluated by using matched batches of eggs for fresh and cryopreserved sperm.

Fish No.	Body length (cm)	Body weight (g)	Testis weight (mg)	Sperm density (×107/ml)	Sperm motility (%)		Cryopreserved sperm			Egg quality with fresh sperm
					Before freezing	After thawing	Eggs used	Fertilization (%)	Hatch (%)	Eggs used	Fertilization (%)	Hatch (%)
1	2.6	0.3567	2.7	2.95	58	37	12	92	83	12	100	92
2	2.5	0.2857	1.5	6.92	36	12	11	100	100	10	100	100
3	2.7	0.3249	3.4	3.78	58	25	12	100	100	11	100	100
4	2.5	0.2768	1.0	0.70	26	5	11	18	18	10	100	100
5	2.4	0.2716	1.9	2.24	32	12	13	85	92	12	92	67
6	2.7	0.4041	2.4	10.25	83	41	10	100	100	10	100	50
7	2.6	0.3646	1.6	10.16	83	20	10	100	70	10	100	80
8	2.4	0.2890	2.1	2.13	74	26	10	90	40	10	100	100
9	2.4	0.3097	2.0	1.81	16	11	10	90	90	10	100	90
10	2.5	0.3061	2.0	3.28	29	18	10	100	100	10	100	80
11	2.6	0.2540	2.2	0.96	66	23	10	100	80	10	90	90
12	2.6	0.3177	2.2	1.41	45	21	10	80	50	10	100	70
13	2.8	0.4026	2.5	2.95	30	28	10	90	90	10	100	100
14	2.6	0.2900	2.0	1.81	35	19	10	80	60	10	100	100
15	2.5	0.2384	2.2	6.40	40	22	10	100	80	10	100	90
16	2.9	0.4318	3.1	2.28	48	22	10	80	80	10	70	70
17	2.3	0.2388	1.2	0.72	5	1	10	10	0	10	90	80
18	2.6	0.2714	2.1	2.78	29	22	10	80	30	10	100	70
19	2.7	0.2970	2.6	3.60	56	26	10	70	70	10	100	100
20	2.7	0.3302	1.2	*	*	*	10	0	0	10	100	100
Mean	2.6	0.3122	2.1	3.53	45	21	10	82	70	10	97	86
SD	0.1	0.0561	0.6	2.87	22	10	1	26	30	1	7	15

^*Fish number 20 not included in calculation of these means and SD because there were no sperm included in this sample.