- LARVAL FEED ALTERNATIVES
- Phil Boeing
|
|
CONTENTS
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INTRODUCTION
There are two major reasons why non-living produced feeds for rearing larvae of aquatic
animals do not yet have an advantage over live food organism. These are:
- rapid deterioration of water quality due to disintegration of micropellets, which are
usually fed in excess in order to achieve satisfactory growth and survival;
- high mortality rates, due to malnutrition and/or incomplete digestion of diet
components.
Cultivation of larval stages of various aquaculture species is still highly dependent
on live food which is for herbivorous larvae, like molluscs and crustaceans, a fairly
understood task. Many more difficulties have to be faced when live food animals are
required, as is mainly the case in fish rearing, but holds true for latter stages of
crustacean larvae as well. The reason why live food is so essential for larval growth has
not yet been clearly defined. Enzymes present in phyto and zooplankton but not synthesized
by the physiological system of a larvae are probably important. Also of importance are
several essential biochemical compounds such as poly-unsaturated fatty acids, most of
which have been defined as to species requirements. Primary producers of these fatty acids
such as algae and bacteria form the base of the trophic pyramid, and as such constitute
the largest link in the aquatic food chain. The large-scale, intensive production of
microalgae and rotifers suffers from two major problems: it is expensive and often
unreliable. Contributing to the problem is the fact that designs used for experimental and
pilot scale units, which are the bulk of the published research, are usually inappropriate
for larger system because of logistical problems, prohibitive cost of materials, or
diminishing surface area to volume relationships which affect scale up performance. Scale
up problems can arise in the bulk handling of materials such as animals, water and feeds
which in a restricted laboratory situation are easily transported and held in small
containers. Carrying out necessary life support functions can also become complicated,
since daily work routines for large numbers of animals quickly becomes prohibitive.
Routine maintenance and cleaning of culture units, while trivial in the laboratory becomes
a major problem with increased scale. As hatchery managers try to stem the rising costs of
production, the economic cultivation of live feeds or some alternative becomes ever more
important. The sections that follow will attempt to illuminate various options and
potentials for larval penaeid shrimp feeds. The summary section will then rate the most
cost effective choices for management consideration.
Top of page
ALGAE
There has been widespread interest in the mass production of microalgae since the
1940's. Microalgae have been cultured as a source of oils, polysaccharides, fine chemicals
and oxygen. They have been exploited for soil conditioning, eutrophication control,
waste-water treatment, and consumption by humans, livestock and aquatic organisms. At one
time, mass culture of algae was seen as a solution to the world protein shortage and
numerous other global problems. In most cases, however, large scale microalgal culture has
fallen short of economic expectations due, in large part, to the expense and difficulties
associated with separation of the cells from the culture medium and processing. A clear
exception to this is the cultivation of microalgae to feed aquatic organisms, i.e., its
use as a feed as opposed to food. In general, the most important problems encountered in
the large-scale production of microalgae as feed for bivalves, crustaceans and rotifers
may be classified as either 1) economic in nature, or 2) related to the dependable output
and consistent quality of large volume production. Algal production costs for aquatic
animals may be determined indirectly by estimating the percentage of total hatchery costs
used to grow algae. Very large volumes of select algae are required for the nursery
culture of bivalve molluscs, while smaller amounts are used in the larviculture of
commercially valuable molluscs and penaeid shrimp. From the data shown in Fig. 1, it is
possible to see that penaeid shrimp hatcheries use more of the total hatchery costs to
produce algae than do bivalve hatcheries.
Fig 1. Percent total hatchery costs
used for algae production, ration of algae culture volume to target species culture
volume.
|
|
USA
Washington (Thalassiosira pseudonana 3H clone; 1990 date) |
- USA
- Hawaii (Nanno-
- chloropsis
- oculata)
|
- USA
- Louisiana
- (chlorella
- minutis-sima
|
USA
Maryland (Unidentified sp.; projections based on 5,000 - 500,00 liter
fermentors |
THAILAND
(Chaetoceros calcitrans) |
N.
CHINA (Isochrysis galbana) |
|
%
Total hatchery operating costs used for algae production
|
- 18 (algae production cost is approx. $50/kg dry weight)
|
- 1/6 labor force devoted to algal production
|
- N/A
|
N/A (production
cost: $2 - 25/kg dry weight) |
Approx. 15% |
1/3 labor force
devoted to algal production |
| Ratio of algae
culture volume: target species culture volume |
1 : 3 (oyster larvae) |
- 4 - 5 : 1
- (rotifers) : 1 (fish larvae)
|
- N/A
|
N/A |
10 : 1 (Penaeus larvae) [calculated from the
total volume of Chaetoceros water used in each batch] |
4 : 1 (Argopecten broodstock) 1
: 2 (Argopecten larvae) |
|
Ranking
of major costs (% total algae production cost)
|
- 1. Labor (37%)
- 2. Overhead (30%)
- 3. Lab supplies & chemicals (19%)
- 4. Energy
|
- 1. Labor
- 2. Energy
- 3. Supplies & equipment
|
- 1. Supplies & chemicals (energy & capital not
included)
|
- 1.Carbon source (15-45%)
- 2.Capital (18 - 30%)
- 3.Other chemicals and equipment (5 - 25%)
- 4.Energy (10 - 20%)
- 5.Labor (2 - 5%)
|
- 1.Chemicals and supplies (35%)
- 2.Labor (24%)
- 3.Matinenance (18%)
- 4.Energy (6%)
- 5.Starter cultures (4%)
|
- 1. Supplies and chemicals (70%)
- 2. Labor (20%)
- 3. Energy and misc. (10%)
|
Top of page
-
|
TAIWAN
- (skeletonema
- costatum)
|
- S. KOREA
- NFRDA
- (Pavlova Lutheri)
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- S. KOREA
- NFUP
- (Nannochloris
- oculata)
|
- SINGAPORE
- (Nannochloropsis
- oculata)
|
- JAPAN
- SNFRI
- (Tetraselmis
- tetrathele)
|
- JAPAN
- NRIA
- (Synecococcus sp.)
|
- % Total
- hatchery operating
- costs used for algae
- production
|
2% |
N/A |
30 - 40% |
25 - 30% |
N/A |
Small |
- Ratio of algae
- culture volume:
- target species
- culture volume
|
- 10 - 15 : 1
- (penaeid larvae)
|
- 5 : 1
- (1 mm spat)
|
- 3 - 4 : 1
|
- 1.5 - 2.0 : 1
|
- 4 : 1
- (Penaeus japonicus larvae)
- 8 - 10 : 1
- (Rotifers)
|
- 5 : 1
|
- Ranking of
- major costs (% total algae
- production cost)
|
- 1. Facility (44%)
- 2. Labor (37%)
- 3. Stock (9%)
- 4. Supplies (6%)
- 5. Energy (4%)
|
- 1. Facility
- 2. Supplies
- 3. Energy
|
- 1. Facilities and supplies (50%)
- 2. Labor (30%)
- 3. Energy (10%)
- 4. Other (10%)
|
- 1. Labor (50%)
- 2. Facilities and equipment (30%)
- 3. Energy (10%)
- 4. Supplies (10%)
|
- 1. Supplies and chemicals (45 - 55%)
- 2. Energy (30-40%)
- 3. Equipment (10-20%)
|
- 1. Supplies and chemicals (60%)
- 2. Labor (20%)
- 3. Energy (20%)
|
Top of page
Another estimate of resources devoted to algal production may be derived from the ratio
of algae culture volume to target species volume. The highest algae : target species
ratios are for penaeid shrimp, which indicates that these facilities probably devote a
great deal more resources to producing algae than to growing shrimp larvae or rotifers.
Why are the economics of shrimp hatchery algae production higher than those of bivalve
hatcheries? The answer lies in the efficiency of the mass algae culture systems used at
these facilities. Most bivalve hatcheries are located in temperate areas where outside
temperatures never exceed high end limits for the species being cultured. Their problem is
one of too little light in the winter months to maintain algal division rates at
acceptable levels. Generally, they have to add light to outside tanks during the winter
months. On the other hand, penaeid shrimp hatcheries are located in tropical and
sub-tropical areas where temperatures are in excess of optimal algae species criteria for
at least half of the average production season. Light is also in excess in these tropical
areas for outside cultures. Rather than design facilities around these environmental
parameters as have in the bivalve hatcheries, shrimp culturists adapt phytoplankton
species to their system irregardless as to whether they are of optimal nutritional value
to the shrimp larvae. As a first step towards designing better production facilities,
shrimp hatchery biologists and engineers need to take a critical look at existing systems,
their yields, operating costs, reliability, etc., and consider ways of improving
performance through better design. Mass algal production systems should be designed around
the most nutritionally sound algae species available for a particular culture organism.
What most penaeid hatcheries do is simply rely on culturing whatever grows best in their
system. In most cases these "weeds" are not the best food for penaeid larvae.
Culture age/growth phase, light intensity, temperature, nutrient limitation and source and
cell density can all affect the chemical composition of the algae. The problem of
consistent nutritional quality is also especially pronounced in outdoor cultures. When
during up-scaling, an algal culture is transferred outdoors, the cells often suffer from
photic shock. This is due to not being adapted to light of such a high intensity, and they
require a period of time to adapt. After this "lag phase' if the algae survives, the
higher temperatures and higher incident light levels in outside cultures generally cause
accelerated growth rates which are not as easily managed as indoor cultures. The pH of the
culture is not maintained within desired ranges and algae is more often than not fed at a
less than optimal nutritional level or past exponential growth rates. Algal cells in
exponential phase may have a different biochemical composition to those in stationary
phase. Changes in basic culture parameters can also change the fatty acid profile of the
algae. It is well known that lipids are the most energy rich of the nutrient classes,
providing approximately 9 Cal/g compared to 4-5 Cal/g for carbohydrates. The principal
components of most lipids are fatty acids. Many marine animals appear to have a limited
ability to synthesize the poly-unsaturated fatty acids (PUFA) 20:5(n-3) or EPA and
22:6(n-3) or DHA from precursor fatty acids in the linolenic acid family. The growth and
survival of penaeid shrimp has been shown to increase when foods rich in EPA and DHA are
included in the diet. The fatty acid profiles of 10 algae species are shown in Fig. 2.
These algaes were grown at 20 degrees C. with 79-80 uE/m2/s2 on 12:12 light:dark cycle
with Guillardīs F2 medium. Three of the species shown were sampled 6 months later under
similar conditions to test whether similar compositional data would be obtained.
Noteworthy here are the 20:5(n-3) and 22:6(n-3) levels in the typical larval penaeid
shrimp algaes C.gracilis, and T. suecica related to the bivalve larval feeds
C. calcitrans, T. isochrysis, and P. lutheri. In a series of
experiments conducted at the Hawaii Institute of Marine Biology, Penaeus vannamei
and Penaeus monodon larvae were fed various phytoplankton species diets and to
evaluate their performance against each other. Larvae fed Thalassiosira weisflogii
had an 82% survival versus 76% survival for larvae fed Chaetocerous gracilis. More
important was the fact the larvae fed Chaetocerous gracilis had a mean dry weight
of 78.6 ug per postlarvae while those fed Thalassiosira weisflogii attained a mean
dry weight of 132.7 ug per post larvae!!!. In separate experiments, mean dry weights of
larvae fed T. weisflogii, exclusively, compared favorably to weights of animals fed
phytoplankton and Artemia.
Top of page
Fig 2. Percentage composition of fatty acids in diatoms and
prymnesiophytes.
Percentage composition of fatty acids
in green algae and Chroomonas
| |
- Green algae
|
- Green algae
|
- Green algae
|
- Cryptomonad
|
- Cryptomonad
|
- Cryptomonad
|
| Saturates |
DUN |
NAN |
TET no.1 |
TET no.2 |
CHRO no. 1 |
CHRO no. 2 |
| 12:0 |
TR |
TR |
0.1 |
0.7 |
0.1 |
TR |
| 14:0 |
0.2 |
0.6 |
0.6 |
0.9 |
8.6 |
8.2 |
| 15.0 |
TR |
0.1 |
0.3 |
0.3 |
0.3 |
0.2 |
| 16:0 |
14.7 |
20.1 |
20.3 |
24.0 |
15.1 |
12.9 |
| 17:0 |
0.1 |
TR |
TR |
0.3 |
0.4 |
0.2 |
| 18:0 |
0.4 |
1.1 |
0.9 |
0.6 |
0.9 |
0.7 |
| 20:0 |
TR |
0.1 |
TR |
- |
TR |
TR |
| 22:0 |
TR |
TR |
0.2 |
TR |
0.1 |
TR |
| 24:0 |
TR |
0.1 |
TR |
- |
TR |
TR |
| SUM% |
15.4 |
22.1 |
22.3 |
26.8 |
25.5 |
22.2 |
| |
- Green algae
|
- Green algae
|
- Green algae
|
- Cryptomonad
|
- Cryptomonad
|
- Cryptomonad
|
| Monounsaturates |
DUN |
NAN |
TET no.1 |
TET no.2 |
CHRO no. 1 |
CHRO no. 2 |
| 16:1(n-10) |
- |
0.5 |
- |
- |
0.2 |
- |
| 16:1(n-9) |
0.1 |
1.3 |
0.9 |
1.2 |
0.1 |
0.2 |
| 16:1(n-7) |
0.1 |
0.6 |
0.3 |
0.3 |
0.5 |
0.6 |
| 16:1(n-5) |
- |
- |
- |
- |
- |
- |
| 16:1(n-13)t |
2.7 |
8.9 |
1.5 |
0.8 |
1.3 |
1.2 |
| 18:1(n-10) |
- |
- |
- |
- |
0.1 |
0.4 |
| 18:1(n-9) |
2.0 |
4.9 |
12.3 |
14.5 |
2.9 |
2.3 |
| 18:1(n-7) |
0.3 |
0.4 |
0.4 |
1.1 |
3.5 |
3.2 |
| 20:1(n-9) |
- |
- |
1.6 |
2.6 |
- |
- |
| SUM% |
5.2 |
16.6 |
16.7 |
20.5 |
8.6 |
7.9 |
| |
- Green algae
|
- Green algae
|
- Green algae
|
- Cryptomonad
|
- Cryptomonad
|
- Cryptomonad
|
| Polyunsaturates |
DUN |
NAN |
TET no.1 |
TET no.2 |
CHRO no. 1 |
CHRO no. 2 |
| 16:2(n-7) |
- |
- |
- |
- |
- |
- |
| 16:2(n-6) |
0.7 |
4.2 |
1.1 |
1.8 |
- |
- |
| 16:2(n-4) |
- |
- |
- |
- |
- |
- |
| 16:3(n-6) |
- |
0.3 |
4.6 |
6.0 |
- |
- |
| 16:3(n-4) |
- |
- |
- |
- |
- |
- |
| 16:3(n-3) |
4.2 |
14.4 |
TR |
0.5 |
- |
- |
| 16:4(n-3) |
21.0 |
- |
13.7 |
7.9 |
- |
- |
| 16:4(n-1) |
- |
- |
- |
- |
- |
- |
| 18:2(n-9) |
- |
- |
- |
- |
- |
- |
| 18:2(n-6) |
4.8 |
10.3 |
13.8 |
13.9 |
11.6 |
10.5 |
| 18:3(n-6) |
2.7 |
TR |
0.7 |
2.7 |
3.0 |
2.6 |
| 18:3(n-3) |
43.5 |
21.7 |
11.1 |
4.6 |
11.9 |
14.2 |
| 18:4(n-3) |
1.0 |
2.7 |
8.4 |
4.8 |
19.8 |
21.3 |
| 18:5(n-3) |
- |
- |
- |
- |
- |
- |
| 20:4(n-6) |
- |
0.5 |
1.5 |
2.1 |
1.0 |
0.9 |
| 20:4(n-3) |
- |
1.1 |
0.3 |
0.1 |
0.9 |
1.0 |
| 20:5(n-3) |
- |
3.2 |
4.3 |
5.3 |
10.9 |
11.9 |
| 22:5(n-3) |
- |
- |
- |
- |
TR |
0.3 |
| 22:6(n-3) |
- |
TR |
TR |
TR |
5.7 |
5.2 |
| SUM% |
77.9 |
59.0 |
59.5 |
49.7 |
64.8 |
67.9 |
| Others |
1.5 |
2.3 |
1.5 |
3.0 |
1.1 |
2.0 |
| TOTAL% |
100.0 |
100.0 |
100.0 |
100.0 |
100.0 |
100.0 |
DUN (dunaliella tertiolecta) / NAN (Nannochloris atomus) / TET (Tetraselmis
suecica) /CHRO (chroomonas salina)
Top of page
- Fig 2. (CONTINUED)
Percentage composition of fatty acids
in diatoms and prymnesiophytes.
| Saturates |
- Diatoms
- C.CAL
|
- Diatoms
- C.GRA no.1
|
- Diatoms
- C.GRA no.2
|
- Diatoms
- SKEL
|
- Diatoms
- THAL
|
- Prymnesiophytes
- T.ISO
|
- Prymnesiophytes
- PAV
|
| 12:0 |
TR |
TR |
TR |
TR |
TR |
TR |
0.3 |
| 14:0 |
17.5 |
8.8 |
11.6 |
20.1 |
14.3 |
16.0 |
11.5 |
| 15.0 |
0.8 |
1.0 |
1.2 |
1.2 |
0.8 |
0.5 |
0.5 |
| 16:0 |
10.7 |
23.3 |
17.8 |
16.5 |
11.2 |
14.5 |
21.3 |
| 17:0 |
0.3 |
0.3 |
0.2 |
0.6 |
0.1 |
TR |
0.2 |
| 18:0 |
0.8 |
4.1 |
3.1 |
0.8 |
0.7 |
0.2 |
1.3 |
| 20:0 |
TR |
0.3 |
0.2 |
TR |
0.1 |
0.3 |
0.3 |
| 22:0 |
TR |
0.6 |
0.6 |
TR |
TR |
0.6 |
0.2 |
| 24:0 |
0.1 |
0.3 |
0.8 |
TR |
TR |
TR |
0.2 |
| SUM% |
30.2 |
38.7 |
35.5 |
39.2 |
27.2 |
32.2 |
35.9 |
| Monounsaturates |
- Diatoms
- C.CAL
|
- Diatoms
- C.GRA no.1
|
- Diatoms
- C.GRA no.2
|
- Diatoms
- SKEL
|
- Diatoms
- THAL
|
- Prymnesiophytes
- T.ISO
|
- Prymnesiophytes
- PAV
|
| 16:1(n-10) |
- |
- |
- |
- |
- |
- |
- |
| 16:1(n-9) |
- |
- |
- |
- |
- |
0.3 |
- |
| 16:1(n-7) |
30.0 |
33.4 |
26.8 |
28.6 |
18.0 |
4.2 |
16.8 |
| 16:1(n-5) |
0.1 |
0.1 |
0.2 |
0.6 |
0.3 |
- |
TR |
| 16:1(n-13)t |
0.7 |
1.2 |
1.6 |
1.3 |
0.4 |
- |
- |
| 18:1(n-10) |
- |
- |
- |
- |
- |
- |
0.3 |
| 18:1(n-9) |
2.8 |
3.6 |
6.0 |
1.4 |
0.5 |
20.1 |
1.7 |
| 18:1(n-7) |
0.2 |
1.7 |
3.9 |
0.1 |
0.1 |
1.3 |
1.4 |
| 20:1(n-9) |
- |
- |
TR |
- |
0.2 |
0.2 |
0.2 |
| SUM% |
33.8 |
40.0 |
38.5 |
32.0 |
19.5 |
26.1 |
20.4 |
| Polyunsaturates |
- Diatoms
- C.CAL
|
| | |