Fish Oil

Advertising’s Role in the Popularity of Fish Oil Fertilizers

Fish oil and emulsion have long been viewed as valuable fertilizers due to the influence of advertising. Over time, marketing shaped public perception, turning a former waste product of the fish rendering industry into something essential for plant health. The belief that fish oil is an effective plant fertilizer remains widespread, though it lacks support from soil and plant science.

What Fish Oil Fertilizers Are Made Of

Saturated fish oil, often used in fertilizers, holds little intrinsic value as a plant nutrient. To classify the product as a legal fertilizer, manufacturers typically add cheap minerals. This process turns what was once disposal-bound waste into a marketable product.

Not All Fish Oils Are the Same

Valuable Unsaturated Fish Oils

Unsaturated fish oils, which remain liquid at room temperature, are used in other industries. These are extracted from fishmeal and sold for specialized purposes. For example, shark oil from dogfish (a non-endangered species) diffuses quickly in water and is used in bait. Despite its specialized uses, this oil offers no benefits for plant nutrition.

Chemical Structure and Plant Use

Oils, including fish oil, consist of chains of carbon atoms—structurally similar to gasoline, diesel, and other fuels. These substances do not serve as plant food. Plants acquire carbon from atmospheric CO₂, which is converted into sugars during photosynthesis. These sugars provide plants with energy, not oils.

Oils and Soil Microbiology

Certain soil microorganisms can break down oils, but the process is slow due to the limited number of microbes that perform this function. Oils are not commonly found in soil organic matter, so nutrients from fish oils are not readily available to plants.

Misunderstandings in Organic Gardening

Fish oil fertilizers are sometimes mistaken for organic products. However, these fertilizers are not certified organic. Their nutrient value comes from added inorganic substances such as urea, nitrate nitrogen, phosphoric acid (which also extends shelf life), and soluble potassium.

Two Common Types of Fish Oil Fertilizers

Type 1: Low-Value Fertilizers

Products in this category typically carry a 5-1-1 NPK ratio. They contain ammoniacal nitrogen, nitrate nitrogen, and urea nitrogen. These low-cost and widely available fertilizers offer 5% nitrogen, 1% phosphoric acid, and 1% soluble potash.

Type 2: Fish Scrap-Based Fertilizers

These fertilizers also carry a 5-1-1 label but state that their nitrogen is “derived from ocean fish.” Rather than using fishmeal, this type includes oils and scraps cleaned from equipment and floors in fish-processing facilities. The scraps undergo steam treatment and acid hydrolysis using hydrochloric or phosphoric acid, which helps liquefy the protein and kill bacteria. When the phosphorus level reaches 1% and chloride 4%, hydrochloric acid is likely used. Although the product contains fish protein, added nitrates and urea legally qualify as a fertilizer.

Alternatives to Fish-Based Fertilizers

Numerous inorganic fertilizers provide the same 5-1-1 nutrient ratio without involving fish oil. These alternatives offer the same nutrients without relying on animal byproducts or waste materials.