Image copyright Danielle Demetriou Image caption Mr Imada says that as a sushi chef "you never graduate, you never stop learning, not until you die"

Yosuke Imada is among Japan's most renowned sushi chefs. Mr Imada, 68, heads Kyubey, a family-run sushi restaurant in Ginza, Tokyo, with branches in Osaka and four major hotels.

My father opened a sushi restaurant in Ginza in 1935. During the Second World War, my family escaped to my father's northern hometown in Akita, and this was where I was born in March 1945.

It was a difficult time to be born. We stayed in Akita until 1946, when my father returned to Tokyo and reopened the sushi shop.

We lived in the same building as the restaurant so it was where I grew up. I was surrounded by sushi from the start.

I knew what I wanted to do from an early age. As young as 10, I remember telling schoolteachers: I will one day become a sushi chef like my father.

I was given a part-time job at the restaurant when I was 16. But I was not allowed anywhere near a sushi knife - I was mostly cleaning or washing dishes.

When I turned 18 - in 1964, an exciting year, with the Tokyo Olympics - I graduated and moved to Kobe to work as a trainee in a sushi restaurant.

It was a good experience living and working in a different place, away from the family business. I learnt a lot and I enjoyed it.

Image copyright Yosuke Imada Image caption The most expensive fish Mr Imada ever bought cost close to $300,000

'Never stop learning'

About 18 months later, I returned to Tokyo and started as an apprentice for my father. It takes at least 10 years to become a sushi chef. You have to be patient. It's a slow system.

What makes a good sushi chef? The most important thing is spirit. You need to understand that you never graduate, you never stop learning, not until you die.

I have been working for more than 50 years. I made sushi yesterday - and I know that today's sushi will be better than yesterday's. It's an endless process. Skill and experience are important but ultimately, your spirit is the most important ingredient.

Today, we have 100 staff in six outlets. I start work in Ginza around 08:00 am. Once a week, I go to Tsukiji fish market with my head chef at 06:30 to obtain information from buyers. Our chefs collect a truck of fresh fish every day.

In the mornings, I have paperwork and meetings. Before customers arrive at around 11:30, I check the kitchens and reservations.

I still make sushi almost every day. I made some just a few hours ago. Some regular customers request that I prepare their sushi.

After lunch, I take a break between 14:00 and 16:00 - sometimes I have a nap, or maybe a quick massage.

Dinner starts at 17:00. Dressed in my white chef's uniform, I greet every single customer, normally around 100 people a night.

We receive many politicians and famous people. I've served Steven Spielberg many times - he is very gentle. But I speak to everyone, not only famous people.

'Family hands'

I enjoy doing this, perhaps because I grew up in the same environment. My parents worked very hard - my father at the sushi bar and my mother serving tea and talking to customers. I watched this unfold every day.

I had a strong respect for my parents and learnt a lot from them, especially my father, who had very famous customers, including prime ministers and artists.

I normally finish around 22:30. It's a long day. But Sunday is always off, as the shop is closed, and during golf season, I sometimes play during the week.

Image copyright Yosuke Imada Image caption Mr Imada trained at a sushi restaurant in Kobe before he joined the family business

Japan is the best place in the world to be a sushi chef. It has very high-quality produce. With warm and cold currents from south to north, there's a good geographical range of fish.

Fishermen's skills are also top class and there is a very speedy distribution system transporting produce to markets.

I have been concerned about Fukushima. We changed our sushi rice from Fukushima to Hiroshima. There are still many government radiation checks for fish so I think it is safe to eat sushi - and luckily, we have not seen a drop in customers.

The most expensive fish I've ever bought was at the New Year auction at Tsukiji a few years ago - around 30 million yen ($294,500, £177,600) for a tuna. We made delicious red sashimi and sushi.

My work can be unusual. I was once flown to a Malaysian island by the Kazakhstan president to prepare sushi for him. We flew everything over, fresh ingredients and rice cookers.

Four years ago, I also prepared sushi for the president's birthday in Kazakhstan. It was an interesting experience but very, very cold - minus 20 or 30 degrees.

In terms of the future? I will not retire. Well, maybe I will half-retire at some point. But I will continue making sushi. My son is a chef here, he's the third generation. I'm happy that the business will carry on in family hands.

Yosuke Imada was speaking to Danielle Demetriou in Tokyo, Japan.