Page 75 - New additives and ingredients in the formulation of aquafeeds

Feasibility
study on
potential
industrial
exploitation
Initial assumptions
The obtaining of enzyme fractions from viscera of different fish species and
its use as an additive in aquaculture feeds to enhance digestibility has been
suggested by several authors (Kollowski, 2001), although results showed
in the present work are the only published evidence of this possibility. In
addition to the biological evaluation, a prospective on the real applicability
of this product should consider financial cost of production at industrial
scale. This aspect is developed in the following section. The main elements
to evaluate are:
· Availability: estimation of the amount of viscera to be obtained from
each fish target species according to their percentage over the weight of
the animal and based on the available statistical data on captures.
· Cost of raw material (viscera): the cost of this by-product should be
estimated like the rest of products exploited by a shipping company.
· Cost of enzymatic extract: it may be estimated considering the yield per
kg of viscera and the costs from the extraction process. Scaling up and
extrapolation must be done to estimate production at industrial scale.
· Impact on the feed price: in terms of relative percentages and depending
on the proportion of enzyme to be added to the feed, it is possible to
estimate the final increase in price of the product. This price increase
greatly depends on the beneficial effects that the modified feed may
have on fish growth and food conversion.
Also, some initial assumptions must be considered:
The starting material to obtain enzymes are the viscera separated on
fishing vessels; more specifically trawl freezer factory vessels working
in multispecific fisheries which systematically gut their catches. Since
they have freezing facilities, they can keep these products under suitable
conditions for further valorisation.
Some species from Great Sole fishing ground could be exploited to a lesser
extent (not all ships have freezing facilities), as well as others from small-
scale fisheries (sardine, hake, horse mackerel and blue whiting), which are
eviscerated by inland processing companies.
The weight of viscera as a percentage of the whole fish varies with the
species from 5% to 12%, so, an average value of 8%was used in the present
study. On the other hand, an average yield of 0.15 kg of CEE or 0.025 kg
of PEE may be obtained from 1 kg of fresh viscera. The estimated annual
production of both products from the viscera of different species is detailed
in Table 5.
Use of purified extracts from fish viscera as an enzyme additive in feeds for juvenile marine fish 73