Feed formulation

1.3.1 General

Successful fish culture depends on supply of diets containing optimal levels of energy and nutrients for growth. Diet preparation is in fact a compromise between the ideal situation and practical considerations (Hardy and Barrows, 2002). The main

CHAPTER 1.GENERAL INTRODUCTION

ingredients to support the maintenance, growth, reproduction and health of the animal at an affordable cost (NRC, 1993). As feed is one of the principle costs in feed production (Lupatsch et al., 2001), formulations must be based on our knowledge of nutritional requirements for them to be economically viable.

In intensive aquaculture, fish feeds are formulated to be dense in nutrients and energy, based mostly on ingredients of marine origin, particularly fish meal and fish oil (Kaushik, 2000). When the requirements of certain fish species are known, it is not difficult to formulate a diet that contains all nutrients at an appropriate level. However, there are practical matters to consider that make this task complicated. The most important of these are the price and the availability of the ingredients, diet acceptability to the farmed fishes, pelletability of the formulation, pellet storage and handling requirements (NRC, 1993). What is also crucial with regard to the aquatic environment, is that the pellets should remain intact in water until fish consume them, while the nutrients should be highly available to the fish (NRC, 1993) to minimize excretions and therefore avoid settlement of organic matter on the bottom with possible impacts on the sediment under and around sea cages (Mente et al., 2006)

1.3.2 Commonly used ingredients and the limitations

The ingredients that are used in fish feed are either by-products of human food technology or products produced directly for fish consumption. Ingredients used in commercial fish diets can be classified as sources of protein (amino acids), fats (EFA), carbohydrates, vitamins and minerals (NRC, 1993). It is also very important to cover the energy requirements of fish, although energy is not considered to be a nutrient in an independent sense.

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CHAPTER 1.GENERAL INTRODUCTION

The main protein source that is used in fish feeds is fishmeal. When prepared from good quality, whole fish it is one of the highest-quality protein sources. Depending on the fishmeal quality, protein level ranges from 56% to 76%, it is also a rich source of energy, EFA and minerals and is highly digestible and palatable to most fishes (NRC, 1993). Fishmeal availability is limited due to somewhat stable production and increased demand (SOFIA, 2006) and thus it is an expensive ingredient (Josupeit, 2008) that contributes greatly to the final cost of fish feeds.

Soybean meal is an available ingredient with high protein content and one of the best amino acid profiles among protein-rich plant feedstuffs for meeting most of the essential amino acid requirements of fish (Mohsen, 1989; quoted in NRC, 1993). It has long been used as a substitute for animal protein in aquaculture feeds. The antinutritional factors (ANF) that are present in soybean seeds and the considerable rise in soybean price over the last year (Josupeit, 2008) are restricting factors for their use in fishfeeds. In addition, the strict rules of EU countries adopted in 2003 relating to the release of genetically modified seeds into the environment, their traceability, labelling and their use in animal feeds (Euractiv, 2006) also proved to be a limiting factor in their use in fishfeeds.

Many other plant protein sources are used, proteins that are extracted from oilseeds such as rapeseed and sunflower, or proteins from cereals like wheat and maize gluten (Aslaksen et al., 2007). Their availability is high, but their use is limited either due to ANF (Aslaksen et al., 2007) or due to imbalanced amino acid profile; for example the lysine deficiency of glutens (Davies et al., 1997; Pereira and Oliva-Teles, 2003).

Fats and oils are the main sources of energy but they also provide the EFA, with marine fish oils containing 10-25% HUFA (NRC, 1993). Marine oils are obtained from

CHAPTER 1.GENERAL INTRODUCTION

processing of marine animals and are classified as fish oils, fish liver oils and marine mammal oils (Hertrampf and Piedad-Pascal, 2000). Their use in fish feeds is restricted by the availability, the high prices (SOFIA, 2006) and the possible contaminants present like dioxins or dioxin-like polychlorinated biphenyls that can be transferred to, and accumulated in, the edible parts of farmed fish (Bell et al., 2005). Plant oils such as soybean, canola (Glencross et al., 2003), linseed (Bell et al, 2004), rapeseed and palm oil (Karalazos, 2007) can be used as substitutes for fish oil, although their fatty acid compositions differ significantly, with vegetable oils containing lower levels of n-3 fatty acids (particularly HUFA) than fish oil. The use of vegetable oils in fish diets can differentiate the fatty acid composition of the produced fish (Bell et al., 2001; 2003), but this effect can be largely overcome after a finishing fish oil diet before harvest (Bell et al, 2004).

Carbohydrate sources such as cereals are present in fish diets as a binder as well as an inexpensive energy source (Davis and Arnold, 1995). Cereal whole grains contain 62-72% starch and this is an important binding agent in steam–pelleted and extruded feeds (NRC, 1993). Many by-products of grain industry as for example wheat, oat, corn, rice, milo or rye by-products are valuable ingredients for animal feeds and subsequently for fish feeds (Hardy and Barrows, 2002). Legumes such as peas, beans and chickpeas contain also considerable amounts of starch that could be utilised by fish as energy source (Booth et al., 2001). The use of these plant ingredients could be limited when their fibre content is high (Nengas et al., 1995) or when they are not processed, as raw starch is considered a poor energy source (Peres and Oliva-Teles, 2002). However, digestibility of raw starch can be enhanced considerably by gelatinization through heat treatment (Peres and Oliva-Teles, 2002) which is a common practice in commercial feeds.

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Other materials that are used in fish feeds in lower quantities are vitamin and mineral premixes, feed binders, carotenoid supplements, drugs and antibiotics, probiotics, enzyme supplements, antifungal agents, antioxidants, fibre, colourings, flavourings and water (Hardy and Barrows, 2002).

1.3.3 The need to identify new/novel feed ingredients

The current general economic and food crisis brought about by increasing oil prices as well as the expansion of the bio-ethanol and bio-diesel industry have generated an unsettled future for food and feed production and prices in general.

Increasing demand, prices and fluctuations in supply in the world markets for fishmeal, fish oil, soybean meal, maize and wheat meal, emphasize the need to reduce their incorporation in feeds and at the same time increase the range of raw material sources.

Fishmeal and fish oil production have been more or less stable over the last few decades (SOFIA, 2006), while events such as the El Ninõ in 1997-1998 have shown that fish oil and meal can become unpredictable raw materials for aquaculture production in specific years.

Furthermore, since European production of soybean is extremely limited, due mainly to climatic and geographical constraints (P.E.A., ÉCLAIR, Programme, 1993;

quoted in Gouveia and Davies, 1998), it is considered worth exploring the possibilities of using other plant sources which are cultivated in European and Mediterranean countries, thus limiting the expense of importation. Peas, chickpeas and faba beans with their protein and starch inclusion levels could successfully replace wheat and partially replace other plant or animal proteins.

CHAPTER 1.GENERAL INTRODUCTION