Vibrio Control — When the Water Glows at Night

If you have walked out at night and seen the water glowing faintly blue, that is luminescent vibrio. It also means the population is already well up. ■ Not a bacterium you remove, one you count Vibrio is native to seawater. You cannot eliminate it from a pond, and elimination is not the goal. The issue is numbers. At low counts nothing happens; when conditions line up and they multiply fast, it becomes disease. So vibrio is judged by how many, not by present or absent. ■ The threshold — 10³ CFU/mL Judge by total vibrio count per millilitre of water. Below 10² CFU/mL is the safe zone. Between 10² and 10³ is the warning zone, where you should start acting. Above 10³ is the danger zone and infection risk climbs clearly. Measurement means culturing water on TCBS agar and counting colonies. Regional fisheries institutes and feed company technical teams often provide this, so it is worth asking. ■ Green colonies are the worse kind On TCBS agar, vibrio grows as yellow or green colonies. The colour splits on the ability to ferment sugar, and in practice the colour is used to grade risk. Green colonies are the more dangerous side. So at the same total count, a higher share of green is the worse situation. When you get results back, do not read only the total — check the colour breakdown too. ■ The glow is an organic matter signal Glowing water means luminescent vibrio has increased, and their increase means there is plenty to eat. The organic matter piled on the bottom is that food. So the first thing to look at after seeing a glow is not a treatment but the bottom and the feed rate. Check whether uneaten feed is being left and whether sludge is accumulating. Attack the bacteria while leaving the cause and they are back in days. ■ Summer speeds them up Vibrio multiplies faster as water warms. That is why vibrio-related accidents cluster in the hot season. The shrimp side worsens at the same time. Water flirting with 34 ℃ already burdens them, and several days near 33 ℃ damages the hepatopancreas. The bacteria multiply fast exactly when the shrimp's defences weaken. ■ Common findings Feed response drops, shells go soft, and more animals look reddish. Rather than mortality spiking overnight, it more often creeps up over several days. Feed intake records make the call much faster here. If intake had been falling for a few days, that is your starting point. ■ Prevention is the environment Dirty the bottom less, leave no feed behind, hold oxygen, and reduce temperature swings. What we call vibrio control comes down to those four. It does not sound like a special measure, but this is the side that actually lowers the count. Disinfection cuts numbers at that moment without changing the conditions. ■ Records matter more than thresholds If weekly testing is hard, at least log feed intake, temperature and bottom condition daily. The conditions that let vibrio grow show up in that record first. The lab result confirms what the record already said. Shrimp365 logs temperature, feed rate and mortality together so you can see the conditions for disease before it arrives. Free to use.