Several methods can be used to count eyed trout eggs. These include measuring volume, displacement, or weight; counting the number of eggs in a V-trough (Von Bayer method); or using electronic egg counters. Many trout farmers use the displacement method to estimate egg volume because it is relatively fast, simple, accurate, and does not require much equipment. The numbers of eggs per unit of volume can be estimated by counting 50 eggs into 25 ml of water in a 50-ml graduated cylinder or burette, and noting the increase in volume. Repeat the process three to five times and calculate the average displacement. The number of eggs per milliliter or per fluid ounce can then be estimated.
To count the eggs using the Von Bayer method:
1. Fill the Von Bayer trough with a single row of eggs (the eggs should fit fairly loosely, but with no spaces between eggs).
2. Count the number of eggs in the trough.
3. Repeat 3 to 5 times to get an average number of eggs per trough.
4. Refer to the Von Bayer chart to determine the number of eggs per ounce or quart.
5. Measure the volume of eggs (number of quarts). Fill a quart container 50% full of water. Using a strainer, add eggs to the container, allowing the eggs to settle by gently tapping the side of the container, until the eggs fill the container and are level at the top. Repeat until all eggs have been measured.
6. Multiply the number of quarts by the number of eggs per quart to determine the total number of eggs. Refer to the Von Bayer chart for estimating the number of eggs.
Number of trout eggs per milliliter or fluid ounce, using displacement measurements. Adapted from Piper et al. 1982. Fish Hatchery Management, U.S. Fish and Wildlife Service and American Fisheries.
| mL displaced by 50 eggs | Eggs per mL | Eggs per fl.oz | mL displaced by 50 eggs | Eggs per mL | Eggs per fl.oz | mL displaced by 50 eggs | Eggs per mL | Eggs per fl.oz | mL displaced by 50 eggs | Eggs per mL | Eggs per fl.oz |
|---|---|---|---|---|---|---|---|---|---|---|---|
|
3.0 |
16.67 | 492.9 |
6.0 |
8.33 | 246.5 |
9.0 |
5.56 |
164.3 | 12.0 | 4.17 | 123.2 |
| 3.1 | 16.13 |
477.0 |
6.1 | 8.20 | 242.4 | 9.1 | 5.50 | 162.5 | 12.1 | 4.13 | 122.2 |
| 3.2 | 15.63 | 462.1 | 6.2 | 8.07 | 238.5 | 9.2 | 5.43 | 160.7 | 12.2 | 4.10 | 121.2 |
| 3.3 | 15.15 | 448.1 | 6.3 | 7.94 | 234.7 | 9.3 | 5.38 | 159.0 | 12.3 | 4.06 | 120.2 |
| 3.4 | 14.71 | 434.9 | 6.4 | 7.81 | 231.1 | 9.4 | 5.32 | 157.3 | 12.4 | 4.03 | 119.3 |
| 3.5 | 14.29 | 422.5 | 6.5 | 7.69 | 227.5 | 9.5 | 5.26 | 155.7 | 12.5 | 4.00 | 118.3 |
| 3.6 | 13.89 | 410.8 |
6.6 |
7.58 | 224.1 | 9.6 | 5.21 | 154.1 | 12.6 | 3.97 | 117.4 |
| 3.7 | 13.52 | 399.7 | 6.7 | 7.46 | 220.7 | 9.7 | 5.16 | 152.5 | 12.7 | 3.94 | 116.5 |
| 3.8 | 13.16 | 389.1 | 6.8 | 7.35 | 217.5 | 9.8 | 5.10 | 150.9 | 12.8 | 3.91 | 115.5 |
| 3.9 | 12.82 | 379.2 | 6.9 | 7.25 | 214.3 | 9.9 | 5.05 | 149.4 | 12.9 | 3.88 | 114.6 |
| 4.0 | 12.50 | 369.7 | 7.0 | 7.14 | 211.3 | 10.0 | 5.00 | 147.9 | 13.0 | 3.85 | 113.8 |
| 4.1 | 12.20 | 360.7 | 7.1 | 7.04 | 208.3 | 10.1 | 4.95 | 146.4 | 13.1 | 3.82 | 112.9 |
| 4.2 | 11.91 | 352.1 | 7.2 | 6.94 | 205.4 | 10.2 | 4.90 | 145.0 | 13.2 | 3.79 | 112.0 |
| 4.3 | 11.63 | 343.9 | 7.3 | 6.85 | 202.6 | 10.3 | 4.85 | 143.6 | 13.3 | 3.76 | 111.2 |
| 4.4 | 11.36 | 336.1 | 7.4 | 6.76 | 199.8 | 10.4 | 4.81 | 142.2 | 13.4 | 3.73 | 110.4 |
| 4.5 | 11.11 | 328.6 | 7.5 | 6.67 | 197.2 | 10.5 | 4.76 | 140.8 | 13.5 | 3.70 | 109.6 |
| 4.6 | 10.87 | 321.5 | 7.6 | 6.58 | 194.6 | 10.6 | 4.72 | 139.5 | 13.6 | 3.68 | 108.7 |
| 4.7 | 10.64 | 314.6 | 7.7 | 6.49 | 192.1 | 10.7 | 4.67 | 138.2 | 13.7 | 3.65 | 108.0 |
| 4.8 | 10.42 | 308.1 | 7.8 | 6.41 | 189.6 | 10.8 | 4.63 | 136.9 | 13.8 | 3.62 | 107.2 |
| 4.9 | 10.20 | 301.8 | 7.9 | 6.33 | 187.2 | 10.9 | 4.59 | 135.7 | 13.9 | 3.60 | 106.4 |
| 5.0 | 10.00 | 295.8 | 8.0 | 6.25 | 184.8 | 11.0 | 4.55 | 134.4 | 14.0 | 3.57 | 105.6 |
| 5.1 | 9.81 | 290.0 | 8.1 | 6.17 | 182.6 | 11.1 | 4.50 | 133.2 | 14.1 | 3.55 | 104.9 |
| 5.2 | 9.62 | 284.4 | 8.2 | 6.10 | 180.3 | 11.2 | 4.46 | 132.0 | 14.2 | 3.52 | 104.2 |
| 5.3 | 9.44 | 279.0 | 8.3 | 6.02 | 178.2 | 11.3 | 4.43 | 130.9 | 14.3 | 3.50 | 103.4 |
| 5.4 | 9.26 | 273.8 | 8.4 | 5.95 | 176.1 | 11.4 | 4.39 | 129.7 | 14.4 | 3.47 | 102.7 |
| 5.5 | 9.09 | 268.9 | 8.5 | 5.88 | 174.0 | 11.5 | 4.35 | 128.6 | 14.5 | 3.45 | 102.0 |
| 5.6 | 8.93 | 264.1 | 8.6 | 5.82 | 172.0 | 11.6 | 4.31 | 127.5 | 14.6 | 3.43 | 101.3 |
| 5.7 | 8.77 | 259.4 | 8.7 | 5.75 | 170.0 | 11.7 | 4.27 | 126.4 | 14.7 | 3.40 | 100.6 |
| 5.8 | 8.62 | 255.0 | 8.8 | 5.68 | 168.1 | 11.8 | 4.24 | 125.3 | 14.8 | 3.38 | 99.9 |
| 5.9 | 8.47 | 250.6 | 8.9 | 5.62 | 166.2 | 11.9 | 4.20 | 124.3 | 14.9 | 3.36 | 99.3 |
Hinshaw, J.M. and S.L. Thompson. 2000. Trout Production: Handling Eggs and Fry. SRAC Publication No. 220.