Effect of Extenders and Osmotic Pressure on Storage of Eggs of Ornamental Common Carp Cyprinus carpio at Ambient and Refrigerated Temperatures

The eggs of ornamental (koi) common carp Cyprinus carpi0 were stored at ambient temperature (∼22–25 C) and at refrigerated temperatures (0–20 C) in extenders at different osmolalities. The treatments evaluated were dry (control), calcium-free Hanks’balanced salt solution (C-F HBSS), salt (NaCl), synthetic ovarian fluid (SOF), and Kurokura #2 (K2). In the first study, eggs were placed in extenders at osmolalities ranging from 130 to 450 mOsmol/kg and were fertilized after 2 h. The percentage of eyed embryos (our measure of fertilization capacity) was calculated 24 h later, and percent hatching was calculated at 60 h. Fertilization capacity of eggs suspended in C-F HBSS (28%) or SOF (37%) was highest (P= 0.0001) at 250 mOsmol/kg, while eggs stored dry (control) had a fertilization capacity of 24%. Fertilization capacity of eggs suspended in NaCl (40%) or K2 (39%) was highest (P= 0.0001) at 200 mOsmol/kg. The percent of eyed embryos and percent hatch were found to be positively correlated (r= 0.9914). In the second study, eggs were stored in these extenders with the most effective osmolality from the previous study to evaluate percent eyed embryos and hatching over time. Samples of eggs were fertilized at every hour for 7 h. Eggs in the extenders C-F HBSS and SOF yielded the highest (P= 0.0001) percent eyed embryos during 7 h. Percent hatch of these eggs was not significantly different (P= 0.1258) among treatments at each time interval. Eggs stored in the extenders SOF, C-F HBSS, and NaCl had higher fertwzation capacity (P= 0.0271) at 7 h than did the dry control. Eggs were also stored at refigerated temperatures in these four extenders at the most effective osmolalities from the first study. A dry control (no extender) was also compared. The third study compared quality of eggs stored for 0, 2, 4, or 6 h in each of the extenders at 5 C or at ambient temperature (∼22–25 C). Eggs suspended in C-F HBSS had significantly higher fertilization capacity at ambient temperature over time than did eggs stored in NaCl, SOF, K2, or the dry control. Eggs suspended in C-F HBSS and the dry control had significantly higher fertilization capacity at 5 C over time than did eggs stored in NaCl, SOF, or K2. Eggs held dry had higher hatch at ambient temperatures (P= 0.0001) and at 5 C (P = 0.0002) over time than did eggs stored in any extender. At 6 h, fertlllvltion capacity with eggs in C-F HBSS or K2 was higher than with NaCl, SOF, or the dry control. The fourth study used C-F HBSS (250 mOsmol/kg) as the extender to evaluate fertilizing and hatching ability during storage at temperatures 0, 5, 10, 15, 20, or 25 C. Eggs were fertilized after 0, 1, 3, 6, 9, or 12 h of storage. Eggs stored at 15 C had significantly higher fertilization capacity (P= 0.0001) than at any other temperature. Eggs stored at 15 C and 10 C had significantly higher hatch (P= 0.0001) than at any other temperature. Fertilization capacity at 12 h was significantly higher in eggs stored at 10 C (33%) or 15 C (29%) than at any other temperature. Storage of koi carp eggs in C-F HBSS at remgerated temperatures extended fertilizing ability for as long as 12 h compared to storage in NaCl, SOF, K2, or the dry control.