Soft-Boned Fish: New Farming Innovation Aims to Make Fish Easier and Safer to Eat

Many people living in Japan are familiar with the struggle of removing bones when eating grilled or simmered fish. A research team from the University of Shiga Prefecture has developed a new farming method that softens fish bones, making them easier to eat.

This innovation enables both children and the elderly to enjoy fish safely while benefiting from its calcium content. The team is currently seeking partners to launch test sales of the fish and will determine future steps based on consumer feedback.

However, there are concerns about potential technology leaks, as the patent for this method has only been filed domestically and not internationally.

Fish has been a staple of the Japanese diet for centuries. It is prized for its high nutritional value, including DHA (docosahexaenoic acid), which is believed to support brain function, as well as its quality protein content.

However, the government's 2023 Fisheries White Paper reveals a significant decline in seafood consumption in Japan. Annual per capita intake has dropped from a peak of 40.2 kilograms in 2001 to just 22.0 kilograms in 2022.

*A rainbow trout with reduced bone density, appearing no different from an ordinary fish. (Provided by Shozo Sugiura)*

Decline of Fish Consumption: The Bone Factor

One of the main reasons for this decline is the inconvenience of dealing with bones in grilled or simmered fish. A survey conducted by the Japan Fishers Association, as noted in the White Paper, revealed that many mothers cited the difficulty of removing bones as the primary reason their children (middle school age or younger) dislike fish.

In response, Professor Shozo Sugiura, a fish nutrition expert at the University of Shiga Prefecture, and his team have developed a method to farm fish with softer bones by altering their feed. While these fish still have bones, their bone density is reduced by about 70%, making them easier to eat.

Testing Various Fish Species

According to Professor Sugiura, in smaller fish around ten centimeters long, the bones are virtually undetectable. In larger fish, the bones are thicker and more noticeable. However, even species up to 20 centimeters long have spines soft enough for children and the elderly to chew without difficulty.

The research team has tested various species, including carp, crucian carp, moroko (a Japanese river fish), rainbow trout, and tilapia. Given the university's Hikone city campus' proximity to Lake Biwa, their focus has been on freshwater fish. However, the method can be applied to saltwater species like farmed horse mackerel, mackerel, and sea bream.

Reducing Phosphorus Absorption

The key to reducing bone density in fish is phosphorus, a substance commonly found in fertilizers. Since bones are primarily made of calcium phosphate, lowering phosphorus intake leads to softer bones.

*Feed developed for farming soft-boned fish. (Provided by Shozo Sugiura)*

To achieve this, Professor Sugiura and his team developed a specialized feed that limits the fish's ability to absorb phosphorus. They began by selecting ingredients with naturally low phosphorus levels. The feed was then washed with an acidic solution to remove even more phosphorus while retaining nutrients.

Additionally, the feed includes an absorbent to ensure that any remaining phosphorus is excreted as waste rather than absorbed by the fish.

The fish only need to be fed this special diet for one to one and a half months before shipping, and they can be raised on regular feed until that time.

Rich in Beneficial Fats

Professor Sugiura is preparing to launch a trial sale of boneless fish, primarily through online channels. He stated that he is "seeking partners for collaboration," and the project's future direction will largely rely on public feedback.

A key feature of these fish is that their bones remain soft when cooked using typical household methods. Additionally, the low phosphorus content in these fish limits their ability to produce adenosine triphosphate (ATP), a compound crucial for converting food into energy.

When this conversion is hindered, fish tend to store more fat, which increases their DHA content. This means these fish are not only easier to eat but also richer in beneficial fats like DHA.

Furthermore, bones are primarily composed of calcium, so consuming the soft bones can enhance calcium intake.

One potential concern is the price, which is currently about 10% higher than that of regular farmed fish. A more significant worry, however, is the risk of this technology being leaked abroad.

In 2023, the research team applied for a domestic patent for the feed production method but has not pursued an international patent due to high costs. Once the domestic patent is granted, the method will be made public.

Professor Sugiura voiced his concern, stating, "There's a risk that boneless fish could be farmed overseas, imported back into Japan, and widely distributed."