A bar grader sorts fish by body width
Small fish slip through the gaps, large ones stay. Choose the gap from the table below.
Grouper, seabass: under 30% spread
Within a lot, the largest fish should be no more than about 30% longer than the smallest. ACIAR's 50 mm grade runs from 45 to 59 mm. No similar rule was found for the other species.
Illustration, not a specific species.
Bar grader table
Table 3 of ACIAR 150: average fish length for each gap. Use 0.5–1 mm steps for small fish and 2 mm steps above about 50 mm.
| Gap (mm) | Orange-spotted grouper (mm) | Tiger grouper (mm) |
|---|---|---|
| 2.0 | 16 | 15 |
| 2.5 | 20 | 18.8 |
| 3.0 | 24 | 22.5 |
| 3.5 | 28 | 26.3 |
| 4.0 | 32 | 30 |
| 5.0 | 40 | 37.5 |
| 6.0 | 48 | 45 |
| 8.0 | 64 | 60 |
| 10 | 80 | 75 |
| 12 | 96 | 90 |
| 14 | 112 | 105 |
How often
| Species | On record | Source |
|---|---|---|
| Seabass | Larval tanks: every 3 days from day 15 after hatching. Nursery tanks, hapas: every 5–7 days | CMFRI 2009, SEAFDEC 2017 |
| Grouper | Every 3 days in Aceh nets; 3–4 days to over a week; every 5–7 days | ACIAR 150, SEAFDEC 2001 |
| Cobia | Every 5 or 7 days above 3 cm; every 10–20 days from 4–5 cm | Nhu 2011, Nguyen Tan Sy 2021 |
| Pompano | Pull shooters at 20–25 days. Short-finned: sample every 3 days early in each step | CMFRI 2024, Hainan 2017 |
| Red drum, rabbitfish | No interval in the sources read | — |
How to do it
1. Prepare
Shallow containers with clean, aerated seawater.
2. Work in small batches
The smallest practical batch, as fast as possible.
3. Move to a clean place
Graded fish go into a disinfected tank or clean net.
4. Watch afterwards
Monitor fish health after grading, since scratches can open the way to disease.
Not yet known
The sources read have no grader table for cobia, pompano, red drum or rabbitfish. The table above is for the two grouper species only.