Q;- What is Bentham’s trout feed and how does it differ from other UK commercial feeds.

A;- At Bentham Trout Farm we have been making feed on farm for our own trout for 20 years. It is made using a conventional mixing and pelleting press as employed by manufacturers of almost all animal feeds and fish feed throughout the rest of the world. In the UK some trout feeds are made by large multi national companies using a more expensive process called extrusion. This came about because we have a large salmon industry in the UK which when profits were high adopted the expensive extrusion process.

Q;-  What are the physical differences between a compressed pellet and an extruded pellet?

A;- A compressed pellet is more dense  in weight and sinks faster. It is ideal to feed to species like trout that feed quickly often in a frenzy. The feed is highly palatable to trout and has a more attractant texture. An extruded pellet is  normally less dense and more porous. This makes it slower sinking and can be made to float and so makes it more suitable to some species of fish. The porosity of an extruded feed is utilised to absorb large quantities of fat. This has become essential to the economic viability of extruded feed. A compressed pellet is much cheaper to produce than an extruded pellet and is gentler to the ingredients because it does not reach such a high temperature. Losses of vitamins and pigments occur during the more aggressive extrusion process.

Q;- How big are the drums and can we handle them.

A; The drums hold 150 kgs. A strong sack truck can move them short distances. Tractor transport boxes are ideal and they can be rolled on their edges on firm ground. The best thing is not to handle them very much. The feed is protected against all weathers and can be left outside by the pondside and the fish fed direct. Alternatively now BTF feed is offered in 500kg big bags and 20/25kg plastic bags.

Q;- Why are BTF  feeds more sustainable.

A;- The extrusion process is an expensive process both in terms of energy  and costs in the process itself, the high capital cost of the plant and the high profit margins required by the shareholders of the multinational companies who run them. These costs exceed the cost of the ingredients, unlike other animal feed where the manufacturing costs rarely exceed 20%.
It is only the ingredients that make fish grow and it follows therefore that the nutrient density of the pellet has to be high to produce a FCR low enough to make the feed economic to use at all. In practice therefore only ingredients of high nutrient density are used in extruded fish feed.
Fishmeal has 70% protein compared with proteins from vegetable origin such as  Soya which have less than 50%. Carbohydrate is far cheaper than oil as a source of nutritional energy for all farmed livestock. However it contains half the energy per unit than oil.
For these reasons Fishmeal and Fishoil are used to excess in extruded feeds. These ingredients are not just expensive but classed as finite and unsustainable even in the short term.
By using a simple compressed pellet, the manufacturing costs are reduced and a least cost formulation adopted which tells us  the most efficient and economic ingredients to use.  As it is with all other forms of livestock feeding. The result of this is that fishmeal and fishoil are minimised because of their expense and replaced with more economic and sustainable vegetable based ingredients.
Extruded feeds are dependent on and exacerbate the high use of of unsustainable fishmeal and oil.

Q;- Can we cut out the use of fishmeal and fishoil altogether.

A. In theory it is possible but in practice not yet. Trout need some fishoil to provide some essential fatty acids but these can be provided by only 5% added fishoil. Vegetable oil and carbohydrate can be used as sources of energy for trout. Since we are using vegetable proteins derived from crops grown for their oil content the obvious thing to do is to leave all or part of the oil unextracted for inclusion in our formulation. As well as oil they also along with some cereal by-products  contain carbohydrate capable of being digested by trout.
Vegetable proteins can replace up to 60% of the protein in trout feeds without any loss of performance. The keyword is balance in all these things.  Trout also use protein for energy with only a proportion of the protein in the diet used for growth, creating body tissue muscle etc. We believe that the right amount of fishmeal to include is that which is used for that growth. In a diet containing 40% protein less than half  is used for growth. In many of the extruded diets most of the fishmeal in the diet is burnt off as energy.

Q;- Are there any sources of high level sustainable proteins that can replace fishmeal kg  for kg in extruded diets.

A;- The perennial question in fish feed. There are a number of novel proteins and processed vegetable proteins that can replace fishmeal. They are used successfully in both fish feeds and mainly young animal nutrition. The problem is that they are and are likely to remain more expensive than fishmeal. In fish feeds the manufacturer who uses these ingredients will always be at a disadvantage to his competitors who use cheaper fishmeal. The change would only come about by legislation to restrict the use of fishmeal.

Q;- What are the implications of either diet for fish health and quality of product.

A;- High fat diets produce fish which are also high in fat, they are only fit to use for the table.  Trout fed a more balanced diet are fitter and healthier and more suitable for re-stocking. They have better muscle texture when filleted and not subject to the same degree of drip loss when smoked.

Q;- What are the implications for the discharge water .

A;- Farms often have varied parameters to which they must comply and often have problems with one parameter whilst the next farmer may have trouble meeting another. Phosphorous and ammonia levels are less because  there is less fishmeal in the diet. The undigested part of vegetable protein passing through the gut is as benign as the dead leaf of a tree in Autumn. Traditional farmers will likely have less difficulty meeting the requirements of their local EA.

Q ;- Which is the most economic way of growing trout and the quickest.

A;- In all trials undertaken by us or others and reported to us the net saving of using BTF feed against an extruded feed is between 10p and 20p per kilogram of trout produced. The growth rate of trout fed on BTF feed is equal to that of extruded feed.