Fish feed is plant or animal material intended for consumption by fish kept in aquariums or ponds. Algae have been used in animal and human diets since very early times. Filamentous algae are usually considered as ‘macrophytes’ since they often form floating masses that can be easily harvested, although many consist of microscopic, individual filaments of algal cells. Algae also form a component of periphyton, which not only provides natural food for fish and other aquatic animals but is actively promoted by fishers and aquaculturists as a means of increasing productivity. Marine ‘seaweeds’ are macro-algae that have defined and characteristic
structures. Microalgal biotechnology only recently began to develop in the middle of the last century but it has numerous commercial applications. Algal products can be used to enhance the nutritional value of food and animal feed owing to their chemical composition; they play a crucial role in aquaculture. Macroscopic marine algae (seaweeds) for human consumption, especially nori (Porphyra spp.), wakame (Undaria pinnatifida), and kombu (Laminaria japonica), are widely cultivated algal crops. The most widespread application of microalgal culture has been in artificial food chains supporting the husbandry of marine animals, including finfish, crustaceans, and molluscs
NECESSITY OF
PRODUCING FISH FEED
The essential nutrients present in the aquatic
bodies are not sufficient for the fishes for pisciculture for the better growth and development as
fishes are cultured in regularly year after year. Thus it causes the depletion
of nutrition in the ponds or other aquatic bodies. As a result of increasing
water pollution, the production of different zooplanktons and phytoplanktons
are also reduced so nutrient deficiency may also occur on that aquatic bodies.
For scientific composite and mixed culture of fishes it is necessary to supply
the sufficient amount of foods for fishes of different feeder level.
Fish foods normally contain macro nutrients,
trace elements and vitamins necessary to keep captive fish in good health. Approximately 80%
of fish
keeping hobbyists feed their fish exclusively
prepared foods that most commonly are produced in flake, pellet or tablet form.
Pelleted forms, some of which sink rapidly, are often used for larger fish or
bottom feeding species such as loaches or catfish. Some
fish foods also contain additives such as sex
hormones or beta
carotene to artificially enhance the color of
ornamental fish.
Using feeds in aquaculture (sometimes referred to as aquafeeds)
generally increases productivity. However, to maximize cost-effectiveness, it
is particularly useful in small-scale aquaculture to utilize locally available
materials, either as ingredients (raw materials) in compound aquafeeds or as
sole feedstuffs.
SOURCES OF FISH FEED
i) Microalgae
as fish feed :-The largest
current application of microalgae feeds is in aquaculture. Microalgae are used
fresh (e.g. live, or at least not dried) in bivalve, shrimp and fish fry and
fingerling production (in the latter case via an intermediate food source, such
as zooplankton or brineshrimp) (Benemann, 1992, Spolaore et al, 2006). Several companies produce aquaculture feeds using Chlorella and Spirulina, or a mixture there of. Some examples of the use of
microalgae for aquaculture:- Microalgae species Hypneacervicornis and Cryptonemia
crenulata particularly rich in protein were tested in shrimp diets (da
Silva et al, 2008). Algae were collected, rinsed, dried and ground up for the
feed formulations. Larvae shrimps were fed daily with one of four diets
prepared
with different percentages of seaweed powder: 39%, 26%, 13%, 0%. The
results suggest that there is an increase in feed conversion when the levels of
algae are increased. Amount of algae in fish feed resulted in significant
increase in shrimp growth rates.
- A large number
of marine nitrogen-fixing cyanobacteria have been tested for their nutritional
value with the hybrid Tilapia fish fry; a majority were acceptable as single
ingredient feeds. Very high growth rates of Tilapia fish using marine
cyanobacteria with in-door and out-door cultures have been reported. The marine
cyanobacterium Phormidium valderianum was shown to serve as a complete
aquaculture feed source, based on the nutritional qualities and non-toxic
nature with animal model experiments (Thajuddin et al., 2005).
Initially, the colour-enhancing
effects of phycocyanin-containing Spirulina biomass or carotenoides from
Dunaliella were exploited in ornamental fish. In recent years, questions
of feed utilization and health status in the dense aquacultural fish populations
became more important. Here, the addition of microalgae can, depending on
concentration, directly enhance the immune system of fish, as investigations on
carp have shown (Schreckenbach et al. 2001).
The addition
of microalga-derived astaxanthin to feed formulations enhances the colour of
the muscles of salmonids. This has a high biotechnological potential and
culture techniques for Haematococcus pluvialis are well developed for
this purpose (Piccardi et al. 1999). On the Hawaiian Islands and in China, Haematococcus
is cultivated in open ponds (Pulz and Gross, 2004).
More than 40
species of microalgae are used in aquaculture worldwide, depending on the
special requirements of local seafood production. In 1999, the production of
microalgae for aquaculture reached 1000 ton (62% for molluscs, 21% for shrimps
and 16% for fish) for a global world aquaculture production of 43 x 106 ton of
plants and animals (Muller-Feuga, 2004).
ii) Macroalgae as fish feed : Spirulina is a blue-green plant plankton rich in raw protein, vitamins A, B1,
B2, B6, B12, C and E, beta-carotene, color
enhancing pigments, a whole range of minerals, essential fatty acids and eight
amino acids required for complete nutrition.
The filamentous green alga (Cladophora glomerata) meal was
used as the sole source of protein for Nile tilapia. Similarly, Appler (1985)
recorded Specific growth rates
of 44 % and 56 % of control diets when the filamentous green alga (Hydrodictyon
reticulatum) meal was used as the sole source of protein for O.
niloticus and T. zillii.
Tacon et al. (1990) used fresh live seaweeds (Gracilaria
lichenoides and Eucheuma cottonii) as the total diet for
rabbitfish in net cages. The brown algae Ascophyllum, Laminaria
and Undaria; the red alga Porphyra; and the green alga Ulva
are also used as fish feed for different types of fishes.
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ALGAL SPECIES FOR COMMON FISH FEED
FISH ALGAE
Catla catla
Fingerlings: Anabanea sp.; Microcystis sp.; Oscillatoria
sp.; spirulina sp. Botryococcus braunii; chlamydomonas sp.; Closterium sp.;
Coelastrum microporum; Eudorina elegan; Pandorina morum; Pediastrum simplex;
Tetrahedron minimum;
Adult: Anabaena sp.; Microcystis sp; Oscillatoria
sp.; Spirulina sp.;
Chlamydomonus.;
Closterium sp.; Coelastrum sp.; Eudorina sp.; Pandorina.; Pediastrum.; Volvox
sp.;
Cyclotella
sp.; Navicula sp.; Pinnularia sp.;
Ceratium.;
Peridinum sp.;
Labeo rohita
Fingerlings: Carteria
sp.; Chlamydomonas sp.; Chlorogonium sp.; Eudorina sp.; Pandorina sp.;
Pleodorina sp.; Volvox sp.;
Closterium
sp.; Staurastrum sp.; Xanthidium sp.;
Adult: Chlorogonium sp.; Closterium sp.; Eudorina
sp.; Gonium sp.; Pandorina sp.; Volvox sp.; Xanthidium sp.;
Botryococcus
sp.;
Mallomonus
sp.; Synura sp.;
Ceratium sp.;
Peridinium sp.;
Anabaena sp.;
Microcystis sp.; Oscillatoria sp.; Spirulina sp.;
CHEMICAL COMPOSITION OF ALGAE
A summary of the chemical
composition of various filamentous algae and seaweeds is presented in Table 2. Algae are receiving increasing
attention as possible alternative protein sources for farmed fish, particularly
in tropical developing countries, because of their high protein content
(especially the filamentous blue-green algae). The dry matter basis (DM)
analyses reviewed in Table 2 show that the protein levels of filamentous blue
green algae ranged from 60–74 %. Those for filamentous green algae were much
lower (16–32 %). The protein contents of green and red seaweeds were quite
variable, ranging from 6–26 percent and 3–29 % respectively. The levels
reported for Eucheuma/ Kappaphycus were very low, ranging from
3–10 %, but the results for Gracilaria, with one exception, were much
higher (16–20 %). The one analysis for Porphyra indicated that it had a
protein level (29 %) comparable to filamentous green algae. Some essential
amino acids is also contained in various aquatic macrophytes.
The lipid levels reported
for Spirulina (Table 2),with one exception (Olvera- Novoa et al.
(1998), were between and 4 and 7 %. Those for filamentous green algae varied
more widely (2–7 %). The lipid contents of both green (0.3–3.2 percent) and red
seaweeds (0.1–1.8 %) were generally much lower than those of filamentous algae.
The ash content of filamentous blue-green algae ranged from 3–11 % but those of
filamentous green algae were generally much higher, ranging from just under 12 %t
to one sample of Cladophora that had over
44 %. The ash contents of green seaweeds ranged from 12–31%. Red seaweeds had
an extremely wide range of ash contents (4 to nearly 47 %) and generally had
higher levels than the other algae.
Nutritional
Quality of Algae : Of the unorthodox feed sources, algae appear to have most
potential for development as an alternative to fish-meal and soybean meal.
Table 2 gives the gross chemical composition of some algal species.
Algae is a
nutritionally-good fish food. Besides the high levels of protein, lipids and
carbohydrates, it contains appreciable amounts of valuable vitamins.
Table 2. Chemical composition (% of dry matter) of selected
algae.
Algae
|
Protein
|
Lipids
|
Carbohydrates
|
Spirulina platensis
|
46 –
50
|
4 – 9
|
8 –
14
|
Spirulina maxima
|
60 –
71
|
6 – 7
|
13 –
16
|
Chlorella vulgaris
|
51 –
58
|
14 –
22
|
12 –
17
|
Chlorella pyrenoidosa
|
57
|
2
|
26
|
Scenedesmus obliquus
|
50 –
56
|
12 –
14
|
10 –
17
|
Scenedesmus quadricauda
|
47
|
2
|
|
Dunaliella salina
|
57
|
6
|
32
|
Synechococcus
|
63
|
11
|
15
|
Euglena gracilis
|
39 –
61
|
14 –
20
|
14 –
18
|
Hormidium
|
41
|
38
|
|
Ulothrix
|
45
|
1
|
Algal lipids are usually
esters of glycerol and fatty acids having C12 to C20. While different algal
groups contain different lipids, the major components include triglycerides,
sulphoquinovosyl diglyceride, monogalactosyl diglyceride, digalactosyl diglyceride,
lecithin, phosphatidyl glycerol, and phosphatidyl inositol. The total lipid
content in algae range from 1 to 40% of dry weight. Cyanophyta contains large
amounts of polyunsaturated lipids, while other groups of algae contain
saturated and monounsaturated fatty acids abundantly.
Besides these, algae contain
pigments like chlorophylls and carotenoids, which make up to 5 % dry weight.
B-carotene is a precursor of vitamin A and is commercially valuable as a colour
enhancer for many species of fish.
The limitation to the use of
algae as feed is the digestibility of the cell wall. For incorporation into
artificial diet, processing of the algal biomass by drum-drying or
freeze-drying can achieve digestibilities up to 90 % (Jauncey, 1982). Studies
on the use of algal meals in artificial diets show that algae is the only
vegetable protein source that can replace fish meal (Becker 1986).
The rate of photosynthesis
in tropical fishponds is about 4gC/m2/day or 30t dry weight
algae/ha/yr (Colman & Edwards, 1987). Assuming a feed conversion ration of
2:1 (dry algae to wet fish), the maximum fish yield is about 15t/ha/yr (Pullin,
1988). If the C:N:P ratio of algal cells is 50:10:1 by weight (Goldman, 1979),
then to maintain the photosynthetic rate of 4 g C/m2/day in a 1 m
deep pond would require daily inputs of 4 g C, 0.8 g N and 0.08 g P per m2
pond area/day.
PRODUCTION OF ALGAE
As in
the case of their environmental conditions, the methods for culturing
filamentous algae and seaweeds vary widely, according to species and location.
This topic is not covered in this review but there are many publications
available on algal culture generally, such as the FAO manual on the production
of live food for aquaculture. Concerning seaweed culture, the following summary
of the techniques used has been has been extracted from another FAO publication
(McHugh, 2003) and further reading on seaweed culture can also be found in
McHugh (2002). Some seaweeds can be cultivated vegetatively, others only by
going through a separate reproductive cycle, involving alternation of
generations.
Where
cultivation is used to produce seaweeds for the hydrocolloid industry (agar and
carrageenan), the vegetative method is mostly used, while the principal
seaweeds used as food must be taken through
the alternation of generations for their cultivation.
WAY OF USING ALGAE
Several feeding trials have
been carried out to evaluate algae as fish feed. Algae have been used
fresh as a whole diet and dried algal meal has been used as a partial or complete
replacement of fishmeal protein in pelleted diets.
1. Algae as major dietary ingredients
The results of the earlier
growth studies showed that the performances of fish fed diets containing 10–20
percent algae or seaweed meal were similar to those fed fishmeal based standard
control diet. Only about 10–15% of dietary protein requirement can be met by
algae without compromising growth and food utilization. There was a progressive
decrease in fish performance when dietary incorporation of algal meal rose above 15–20 %. However,
although reduced growth responses were recorded with increasing inclusion of
algae in the diet, the results of feeding trials with filamentous green algae
for O. niloticus and T. zillii indicated that SGR of 60–80
percent of the control diet could be achieved with dietary inclusion levels as
high as 50–70 percent.
Algae
|
Inclusion
level
(%t)
|
Fish
species
|
Effect
|
Red algae
Porphyra yezoensis
Porphyra spheroplasts
|
5
|
Red sea bream
|
Increased growth, feed
efficiency and protein deposition. Elevated liver glycogen and triglyceride
accumulation in muscle Mustafa et al. (1995)
urvival, growth and
nutrient retention significantly higher than control Kalla et al. (2008)
|
Green algae
Ulva
conglobata
Ulva pertusa
Ulva pertusa
|
5
5
5
|
Nibbler
Black sea bream
Red sea bream
|
Improved growth Nakazoe et al. (1986)
Ulva meal diets repressed lipid accumulation
in intraperitoneal body fat without loss of growth and feed efficiency. Fish
fed 2.5, 5 and 10 % Ulva meal did not show significant body weight loss
during wintering. During starvation, lipid reserves were preferentially
mobilized for energy Nakagawa et al. (1993)
Demonstrated a decrease in susceptibility to
Pasteurella piscicida, an elevation of phagocytosis and spontaneous
haemolytic and bactericidal activity. Satoh, Nakagawa and Kasahara (1987)
Increased growth, feed efficiency and
protein deposition. Elevated liver glycogen and triglyceride accumulation in
muscle Mustafa et al. (1995)
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Recent work by Kalla et
al. (2008) appears to indicate that the addition of Porphyra spheroplasts
to a semi-purified red seabream diet improved SGR. In addition, Valente et
al. (2006) recorded improvements in SGR when dried Gracilaria
busra-pastonis replaced 5 or 10 % of a fish protein hydrolysate diet for
European seabass.
Total replacement of
fishmeal by algal meal showed very poor growth responses for O. niloticus (Appler
and Jauncey, 1983; Appler, 1985) and T. zillii (Appler, 1985). Appler
and Jauncey (1983) recorded a SGR of 58 % of control diet when the filamentous
green alga (Cladophora glomerata) meal was used as the sole source of
protein for Nile tilapia. Similarly, Appler (1985) recorded SGRs of 44 % and 56
% of control diets when the filamentous green alga (Hydrodictyon reticulatum)
meal was used as the sole source of protein for O. niloticus and T.
zillii. Tacon et al. (1990) used fresh live seaweeds (Gracilaria
lichenoides and Eucheuma cottonii) as the total diet for
rabbitfish in net cages. Pantastico, Baldia and Reyes (1985) reported that
newly hatched Nile tilapia fry (mean weight 0.7 mg) did not survive at all when
unialgal cultures of Euglena elongata and Chlorella ellipsoidea were
fed to them.
2. Algae as feed
additives
The main applications of
microalgae for aquaculture are associated with nutrition, being used fresh (as
sole component or as food additive to basic nutrients) for colouring the flesh
of salmonids and for inducing other biological activities (Muller- Feuga,
2004). Several investigations have been carried out on the use of algae as
additives in fish feed. Feeding trials were carried out with many fish species,
most commonly red sea bream (Pagrus major), ayu (Plecoglossus
altivelis), nibbler (Girella punctata), striped jack (Pseudoceranx
dentex), cherry salmon (Oncorhynchus masou), yellowtail (Seriola
quinqueradiata), black sea bream (Acanthopagrus schlegeli), rainbow
trout (Oncorhynchus mykiss), rockfish (Sebastes schlegeli) and
Japanese flounder (Paralichthys olivaceus). Various types of
algae were used; the most extensively studied ones have been the blue-green
algae Spirulina and Chlorella; the brown algae Ascophyllum,
Laminaria and Undaria; the red alga Porphyra; and the
green alga Ulva. Fagbenro (1990) predicted that the incidence of
cellulase activity could be responsible for the capacity of the catfish Clarias
isherencies to digest large quantities of Cyanophyceae.
3. Green water technology : Green
water is a technique of adding microalgae to the
aquaculture / medium where
fishes grown as an enhancement, not as a direct food source.The most commonly
used microalgae for creating green water id Nannochloropsis,
Pavlova and Isochrysis can also
be used if there is adequate circulation.These algae reduce the pollutants of water
and also added high amount of O2 during their photosynthesis. The
use of green water reduces mortality of fish and excels fish health.
PROBLEMS IN USING MICRO ALGAE AS
AN FISH FEED
The algae which
are used as fish feed sometimes may create a problem due to their low
digestibility.Only about 10-15 % of dietary protein
requirement can be met by algae in test diets without compromising growth and
food utilization. There is a progressive decrease in fish performance when
dietary incorporation of algal meal rises above 15-20 %. Total replacement of
fishmeal by algal meal generally shows very poor growth responses. Apart from
commonly observed impaired growth, the use of algae as the sole source of
protein in fish feed can also result in malformation.
The
poor performance of fish fed diets containing higher inclusion levels of algae
may be attributable to high levels of carbohydrate, of which only a small
fraction consists of mono- and di-saccharides. A preponderance of complex and
structural carbohydrates may cause low digestibility.
The
collection, drying and pelletization of algae require considerable time and
effort and algal cultivation is costly. Cost-benefit analysis is needed before
any definite conclusions on the future application of algae as fish feed can be
drawn. The use of algae as fish feed additives may be limited to the commercial
production of high value fish.
In order to
overcome or reduce the problems and limitations associated with algal cultures,
various investigators have attempted to replace algae by using artificial diets
either as a supplement or as the main food source. Different approaches are
being applied to reduce the need for on-site algal production, including the
use of preserved algae, micro-encapsulated diets, and yeast-based feeds. There
is further scope to develop the sector by introducing better quality products,
since it is widely acknowledged that existing concentrated microalgae products
still do not match live microalgae for hatchery applications.
CONCLUSION
Micro algal biotechnology
only really began to develop in the middle of the last century but it has
numerous commercial applications. Algal products can be used to enhance the
nutritional value of food and fish feed owing to their chemical composition;
they play a crucial role in aquaculture. Moderate growth responses and good
food utilization were generally recorded when dried algal meal were used as a
partial replacement of fishmeal protein. However, the collection, drying and
pelletization of algae require considerable time and effort. Furthermore,
cultivation costs would have to be taken into consideration. Therefore, further
cost-benefit on-farm trials that take these costs into consideration are needed
before any definite conclusions on the future application of algae as fish feed
can be drawn.
Nevertheless, the results of
various research studies show that algae as dietary additives contribute to an
increase in growth and feed utilization of cultured fish due to efficacious
assimilation of dietary protein, improvement in physiological activity, stress
response, starvation tolerance, disease resistance and carcass quality. In fish
fed algae-supplemented diets, accumulation of lipid reserves was generally well
controlled and the reserved lipids were mobilized to energy prior to muscle
protein degradation in response to energy requirements.
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