Fermented Fish-Based Liquid Fertilizer: Processing Principles and Quality Control

In short: Fish liquid fertilizer is made by fermenting fish or fish by-products (heads, guts, bones) with molasses and a microbial starter for 3–6 weeks, giving a liquid rich in nitrogen and amino acids. Ferment in a closed container with a gas vent, stir regularly and keep it away from living areas. Dilute about 1:100–1:200 for soil drenches, mainly during leafy growth.

Ingredients

Ingredient	Suggested amount
Fresh trash fish or fish by-products	10 kg
Molasses	2–3 kg
Microbial starter (lactic bacteria, Bacillus…)	As labelled
Clean water	Enough to cover
Plastic drum with lid and gas vent	30–50 litres

Fermentation steps

1. Chop or mince the fish; never use spoiled fish or fish treated with preservatives.
2. Mix with molasses and starter, add water to cover.
3. Close, leaving a quarter of the drum empty; vent gas daily in the first week.
4. Stir every 2–3 days; ferment 3–6 weeks depending on temperature.
5. Ready when the fish has almost dissolved and the smell is sour with a mild fishy note, not putrid. Strain.

How to use it

• Dilute about 1:100–1:200 and drench every 7–10 days.
• Use mainly during leafy growth and recovery after cutting; reduce before harvest.
• For leafy vegetables, stop at least 7–10 days before harvest.

Quality and safety

• Keep the drum away from houses and water sources; seal against flies.
• Wear gloves and wash hands afterwards.
• For larger farms, have nitrogen and microbial content tested before regular use.

FAQ

Does the smell go away?

With enough time, molasses and microbes, the smell drops a lot but a mild fishy note remains. Apply in the cool evening and water in afterwards.

How is it used on mint?

During days 8–35 of the 60-day schedule.

Further reading

• Fermented banana peel liquid
• Home composting: a 30-day framework
• 60-day nutrient schedule for SW88 mint