GB2285907A - Feed for fish fry - Google Patents

Abstract

A soft dry feed is especially for use as weaning feed for fry, at the transition from living feed to formulated feed. It consists of hard roe-like agglomerated particles, which are made of milled or ground fish meal having an average particle particles size below 50 mu m a fat, a bonding agent, and optionally vitamins and minerals. The feed has a water content of below 14% by weight.

Description

"Feed for Fish Fry" This invention relates to feed for fish fry. It is concerned with soft dry feed, especially a weaning feed, for use for fry at the transition from living feed to formulated feed.

The breeding of salmon and trout has gone on in Norway for many years, and such breeding has become a significant industry. In recent years there has also been interest in the breeding of types of marine fish, which can only live in sea water, such as halibut, turbot and cod. The problems with the feeding of larvae and fry of such kinds of marine fish are however substantially greater than the problems with the feeding of larvae and fry of salmon and trout.

Fry of halibut and other types of marine fish are initially fed with edible animals, such as artemia craw fish and rotatoria. After a period of feeding with living feed, one can go over to a formulated feed, which in the trade is often called weaning feed.

Our co-pending Application No. 9318906.6 is concerned with feed and a process for the production of it for the first stage. This Application is concerned with the second stage.

According to the present invention there is provided soft dry feed, especially for use as weaning feed for fry at the transition from living feed to formulated feed, having a water content of less than 14% by weight and optionally containing vitamins and minerals having a particle size of 0.2-1.5 mm, characterised in that it consists of hard roe like agglomerated particles made of milled or ground fish meal having an average particle size (d50) of below 50 Am, fat in an amount of 15-35% by weight, and bonding agent.

Preferably the particle size will be in the range 0.2 1.5 mm.

Conveniently the bonding agent is in the form of a glue water concentrate which forms a gel on cooling down to a temperature in the region from +2"C to +4 C.

When halibut fry or other marine types are to be weaned from feeding with edible animals at the fry stage, specific requirements must be placed on the weaning feed, particularly from the type and development stage. That is to say the weaning feed ought to have the correct content of protein, fat and carbohydrate, have a correct mineral and vitamin content, have a suitable particle size, and the particles ought to be soft and free of sharp particles, which can damage the digestive system. Furthermore the particles ought to retain their shape during feeding, give the desired low leakage to the surroundings and have a satisfactory speed of sinking.

With the starting point in the enriched feed such as that forming the subject of Application 9318906.6, a soft dry feed was produced which satisfied the aforementioned requirements.

The feed consisted of the following ingredients: a) milled or ground meal of corresponding type and quality as was employed for the enriched feed, b) marine fat (cod liver oil and fish oils) or marine fat combined with vegetable fat, c) vitamins and minerals, d) glue water concentrate of high quality (is gelforming in the region +2 to +40C).

Tests were also made by mixing taste attractants, without this having a negative effect on the feed production.

With these ingredients several types of soft dry feed were produced containing less than 12% by weight water, without carbohydrates, and in the form of hard roe-like particles of 0.2 - 1.5 mm magnitude.

Experimentally one found that the fat content in the feed could be varied freely in the region 15-35%. Furthermore it was found that when only raw fish oil is employed, the content of free fatty acids ought to be lower than 1.5%.

The feed retained its shape in the breeding vessels and gave little leakage to the surroundings (10-20% by weight after 30 minutes in water).

From the experiments made it was demonstrated that halibut fry in two breeding installations clearly preferred this feed over commercial weaning feed.

During the feeding the halibut fry snapped at the soft dry feed immediately, in contrast to commercial weaning feed which was spat out again several times before the halibut fry finally managed to swallow it.

In order to achieve the desired particle form and softness there was employed a so-called agglomerating technique. It involves smaller particles being built up into larger particles by means of cutting forces and bonding agents which are either supplied separately or which are present in the particles/powder.

Factors which have significance if one is to succeed with the agglomerating technique are as follows: - Particle size and form for the primary particle versus the agglomerated particle - Which bonding agents which are naturally present, or which must be supplied to the particles during the agglomerating - How and with what strength the cutting forces are supplied to the powder material which is to be agglomerated.

Of known agglomerating methods rotating plates, rotating knives, and air/gas-whirling technique (fluidising) can be mentioned.

The most important supposition is that the choice of mode of milling or grinding, particle size and quality of meal and glue water concentration, together with the necessary amount of fat, yields an agglomerateable material, without the addition of foreign substances. This is achieved by preserving the natural collagens of the fish through the fish meal process.

Tests demonstrate that the agglomerated soft dry feed is reformable after mechanical loading. Deformation of the soft feed by pressure only required that one undertook a little stirring of the powder material, whereby the hard roe-like agglomerates were reformed.

The agglomerating technique functions better the finer the meal is milled or ground. It has been shown that powder with an average particle size, d50, of over 50 Am gave poorer agglomeration.

The advantages of using the soft dry feed, for example as weaning feed, can be summed up as follows: - The halibut fry preferred the soft dry feed over commercial feed in experiments undertaken with two different breeders. Subsequent drying, which is necessary when using known feed products, yields harder particles, together with the danger of oxidising and/or interaction between fat and proteins. The soft dry feed on the other hand need not be subsequently dried.

- The survival and quality of the halibut fry proved to be very good with the breeder which employed the soft dry feed as weaning feed. The high survival achieved by halibut fry must be attributed to the quality of the feed. There were no sharp bone particles in the feed, something which otherwise could damage the digestive system of the fry, and this can be one of the reasons for the high degree of survival.

- The feed included no carbohydrates.

- The fat became mixed into the feed at low temper atures.

With this the danger of the fat-protein interaction and oxidising could be reduced significantly.

It is important that the particle or particles, which the fry consume, must include the right nutrient substances.

Viewed statistically an agglomerated particle of a finely milled or ground meal will include a richer selection of nutrients than a chance meal particle having the size of the agglomerate. Both types of particle will displace the same volume in the digestive system of the fry. The volume of the digestive system defines the feed intake of the fish fry.

Claims (3)

1. Soft dry feed, especially for use as weaning feed for fry at the transition from living feed to formulated feed, having a water content of less than 14% by weight and optionally containing vitamins and minerals having a particle size of 0.2-1.5 mm, characterised in that it consists of hard roe-like agglomerated particles and are made of milled or ground fish meal having an average particle size (d50) of below 50 m, fat in an amount of 1535% by weight, and bonding agent.

2. Soft dry feed in accordance with Claim 1, characterised in that it has a particle size of 0.2 - 1.5 mm.

3. Soft dry feed in accordance with claims 1 or 2 characterised in that the bonding agent is in the form of a glue water concentrate which forms a gel on cooling down to a temperature in the region from +2"C to +40C.