24/12/2025
Separating catfish by size (known as sorting or grading) is essential because catfish are natural cannibals. Larger "jumpers" will prey on smaller ones, and uneven sizing leads to poor feed distribution.
1. Preparation (24 Hours Before)
🌲Stop Feeding: Do not feed the fish for at least 24 hours before sorting. This reduces their stress levels and prevents them from vomiting, which would pollute the water during the process.
🌲Ready New Tanks: Ensure the receiving tanks/ponds are filled with clean, oxygenated water.
🌲Anti-Stress: Adding an anti-stress agent or a small amount of salt to the water can help the fish cope with the handling.
2. Equipment Needed
🌲Grading Boxes/Baskets: These have specific bar spacings or mesh sizes that allow small fish to swim through while retaining larger ones.
🌲Soft Nets: Use knotless nylon nets to prevent injuring the fish’s skin or protective mucus layer.
Large Plastic Bowls/Tanks: For temporary holding.
3. The Sorting Process
There are two main ways to do this:
A. Manual Sorting (For smaller quantities)
🌲Drain the Pond: Lower the water level so the fish are concentrated in a small area.
Catch and Inspect: Use a net to bring a small group of fish into a large bowl of water.
🌲Visual Selection: Manually pick out the "shooters" (exceptionally large ones) and the "runts" (very small ones), placing them into separate containers.
B. Mechanical/Box Grading (The professional way)
🌲Select the Grader: Choose a grading box with bar spacings appropriate for your target size.
🌲The "Dip and Shake" Method:
Place the grader inside a water-filled tank.
Pour a batch of fish into the grading box.
Gently move the box up and down in the water.
Small fish will swim through the bars into the tank.
Large fish will remain inside the box.
🌲Transfer: Move the large fish to their designated pond and collect the smaller ones for theirs.
4. Post-Sorting Care
🌲Disinfection: After sorting, you can give the fish a quick "salt bath" or use a mild disinfectant to prevent infections on any scratches they might have picked up.
🌲Wait to Feed: Do not feed them immediately after sorting. Wait 4–6 hours (or until the next morning) to allow them to recover from the stress.
you should follow a consistent sorting schedule based on the age and size of the fish.
💗Fry and Fingerling Stage (Weeks 1 to 4)
At this stage, catfish grow at vastly different rates. The larger ones, often called "shooters," will quickly begin to eat their smaller siblings if not moved.
🌲Frequency: Every 7 to 10 days.
🌲Focus: Removing the few exceptionally large fish that are outgrowing the rest of the batch.
💗Juvenile Stage (Weeks 5 to 10)
Once the fish reach the juvenile stage, their growth remains rapid, but they are slightly more resilient. However, size gaps can still lead to "tail-nipping" and competition for feed.
🌲Frequency: Every 2 to 3 weeks.
🌲Focus: Dividing the population into three distinct groups: Small, Medium, and Large. This ensures that when you throw feed, the smaller fish aren't bullied away by the larger ones.
💗Post-Juvenile to Table Size (Month 3 Onward)
As the fish approach maturity, their growth rate stabilizes compared to the early weeks. Cannibalism is less of a risk now, but size uniformity is still important for market value.
🌲Frequency: Every 4 to 6 weeks.
🌲Focus: Identifying "slow growers" that may need high-protein "booster" feed and ensuring the largest fish are ready for early harvest or "cropping."
OISAFARM 🇳🇬 Ugwuoba Enugu
