What size should a lot be
From QCVN 02-36:2021/BNNPTNT. Seabass, rabbitfish and hybrid grouper are not covered.
| Species | Small fingerling, cm | Small fingerling, g | Fingerling | Reference age (days) |
|---|---|---|---|---|
| Brown-spotted grouper | 1.5 to under 7 | 1 to under 6 g | from 7 cm, from 6 g | 30 / 70 |
| Cobia | 4 to under 10 | 2 to under 8 g | from 10 cm, from 8 g | 20 / 60 |
| Pompano, long-finned (T. blochii) | 2 to under 5 | 0.8 to under 6 g | from 5 cm, from 6 g | 25 / 35 |
| Pompano, short-finned (T. ovatus) | 2 to under 5 | 0.8 to under 7 g | from 5 cm, from 7 g | 25 / 35 |
| Red drum | 3 to under 5 | 1 to under 4 g | from 5 cm, from 4 g | 35 / 45 |
Age: the first figure runs from first feeding to the small fingerling stage, the second from the end of that stage to the fingerling stage, both reference minimums. Deformity: at most 2% for small fingerlings and 1% for fingerlings.
Lot check on arrival
Balancing temperature and salinity
Each source covers a different situation, so pick the right one.
| Situation | How | Source |
|---|---|---|
| Sealed bag on arrival | Float the bag 10–15 minutes (15–20 elsewhere in the guide), open it to let water in slowly, tilt so fish swim out. Never tip them in. | Quang Ninh 2026 |
| Open tank | Replace 10–15% of the water every 5–7 minutes for about 25–30 minutes. | Quang Ninh 2026 |
| Large salinity gap | Ask the hatchery to adjust until the gap is within ±5‰. Do not change more than 5‰ a day. | Quang Ninh 2026 |
| Wild grouper fry | Farm rule: 1‰ and 1 °C per 30 minutes, usually 30 minutes to 2 hours. | Juario 1996 |
| Red drum | At least 1 hour per 5.6 °C, per pH unit or per 10‰. | SRAC 0324 |
Stock when cool, 06:00–08:00 or 16:00–17:00. Do not pour transport water into the tank.
Quarantine
Hold apart
The Law on Fisheries requires nurseries to have a place to isolate and monitor new seed. One tank and one set of tools per lot.
How long
Guidance on white spot suggests 3–6 weeks at 24–27 °C. For Amyloodinium, VM90 (1994) says at least 3 weeks, and SRAC 4705 (2011) says even 30 days may not be enough. Short nursery cycles must balance this against parasite life cycles and farm scale.
A certificate is no guarantee
Sampling assumes 10% prevalence, for example 27 fish from a stock of 1,000 to 1 million. In Quang Ninh in 2025, a lot that had passed quarantine still fell sick.
Rules to know
Moving seed out of a province needs quarantine registration (Circular 03/2026/TT-BNNMT). Nervous necrosis testing applies to grouper, seabass and cobia. Rules changed a lot in 2026, so ask your provincial Department of Agriculture and Environment before filing nursery papers.