This is a basic expanation on how you can evaluate Fish feed or any sort of feed. Here basically 4 basic types of method of evalution process has been discussed.

1. FEED EVALUATION TECHNIQUES
Introduction:
Fish is the most important protein source for human consumption. Feed is
very important thing for the proper development of fish. Feed is the most
expensive single item used in intensive fish culture systems, representing up
to 60% of fish production cost.
Objective:
Feed evaluation is needed to check the accuracy of the manufacturing process.
It is done:
➢ To measure nutrient loss during manufacturing and storage
➢ To prevent the nutritional value of a particular formulation
➢ To measure the feeding value of formulation
Methods:
A. Physical method
➢ Physical method is used to determine physical characteristics of a
product.
This includes:
➢ Touching: An experienced person can detect the gross defects of
feed by touching the feed grains.
➢ Smelling: By sensing smell, an expert can detect the rancidity and
off odors of the feed.
➢ Tasting: By tasting, off flavor and ingredients’ ratio can be detect.
➢ Sighting: By close observation it is done to detect the stone, pieces
of wood, mold growth etc.
➢ Water stability: Measured by testing the feed in to definite water
flow for certain time.

2. B. Chemical method
Chemical method of diet evaluation includes;
1. Moisture
2. Proximate analysis
i. Crude protein analysis
ii. Crude lipid
iii. Carbohydrate
iv. Ash
C. Chemical tests
1. Moisture:
The water content or moisture of feed is determined by drying a sample
in a drying oven until a constant weight is reached.
The difference between the initial weight of the sample and the weight
after drying is the weight of moisture.
% Moisture=
𝑊𝑡. 𝑜𝑓 𝑟𝑎𝑤 𝑠𝑎𝑚𝑝𝑙𝑒−𝑊𝑡.𝑜𝑓 𝑑𝑟𝑖𝑒𝑑 𝑠𝑎𝑚𝑝𝑙𝑒
water sample
× 100
It is mentionable that, water vapor temperature is 100c, there for to complete
dehydrate the sample, oven temperature should be set up with (100+5) ®c.
2. Proximate analysis:
Proximate analysis is a partitioning of compound in a feed into different
categories based on chemical properties of compounds.
i. Crude protein analysis:
Crude protein is determined by “Micro Kjelahl Method” in which nitrogen
content is directly measured and converted into protein using a conversion
facto.

3. On average protein contain 16% nitrogen. So nitrogen content is multiplied by
6.25(100/16) to calculate protein content.
In this method nitrogen is determined by
%of N =
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑟𝑒𝑎𝑔𝑒𝑛𝑡 ( 𝐻𝐶𝑙 )𝑖𝑛 𝑡𝑖𝑡𝑟𝑎𝑡𝑖𝑜𝑛 ×0.019
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒
× 100
Therefore, crude protein,
% of protein= % N × 6.25
ii. Crude Lipid:
Crude lipid refers to the lipid soluble materials in a sample that can be
extracted with a nonpolar solvent, such as petroleum ether, chloroform, or
alternately supercritical CO2. Using ether a Soxhlet or Goldfish extraction
apparatus, the dry sample is extracted with a hot solvent. After extraction the
solvent is evaporated and the extracted material is weighed. This procedure is
least accurate of the proximate analysis methods.
iii. Ash and mineral:
The category in which inorganic materials that remains after a sample is
burned at 600c is counted as ash.
600c is sufficient enough to burn the organic materials in a sample. Generally
an “Electric Muffle furnace” is used to burn sample.
The ash category contains
❖ Essential elements ( minerals )
❖ Non-essential elements
❖ Toxic elements
iv. Crude Fiber:
Crude fiber measures the material remaining in a sample after it has been
boiled in a weak acid, followed by boiling in a weak base, minus the inorganic
residue (ash).

4. Carbohydrates that are removed from the sample by this procedure are
considered those that would be digested by an animal and those that are left
ate considered complex carbohydrates that are indigestible.
3. Chemical test:
To manufacture high quality diets, one must use high quality ingredients.
The trick is to be able to identify high quality ingredients. The chemical
tests for diet quality discussed below are commonly used to measure
ingredient quality, although they may also be used to test diet quality.
a. Protein quality:
The following chemical tests for protein quality are used to measure the
effects of processing on protein quality.
a.1. Pepsin digestibility:
For years, the fish feed industry has relied upon the pepsin digestibility
test, to detect the fish meal that have been subject to thermal abuse
during their manufacture. This test relies upon the enzyme pepsin,
usually obtained from pig stomachs, to digest the protein in the fish
meal. If the protein has been damaged by thermal abuse during drying,
the pepsin digestibility will be lower than the values typically obtained
with high quality fish meal. Anderson et al (1993), reported pepsin
digestibility values of 97.7, 96.8 and 98.5% for menhaden, anchovy, and
Norse LT-94 fish meal, respectively.
a.2. Available Lysine:
When protein containing lysines are heated in the presence of reducing
sugar, a reaction occurs between the nitrogen of lysine and the reducing
sugar, producing a complex that is indigestible by animals. Amino acid
analysis will show the lysine to be present but is unavailable. The
amount of available lysine can be determined and compared to the total
lysine to judge the quality of the protein source (AFIA 1999).

5. a.3. TVN and Ammonia Nitrogen:
Both TVN and ammonia nitrogen are values that are used to determine
the freshness of raw material used to make fish meal. Because both are
volatile, they are lost during fish meal drying. Nevertheless, these test
are sometimes used to estimate the quality of dried fish meal. The TVN
is sometimes called the total volatile base (TVB). Ammonia-nitrogen and
TVN are measured using Kjeldahl distillation unit ( AFIA 1999).
b. Lipid quality:
The two concerns with lipid are hydrolytic and oxidative rancidity. Both
are undesirable in dietary lipid and in finished feeds.
b.1. Hydrolytic Rancidity:
Hydrolytic rancidity is caused by enzymatic hydrolysis of fatty acids
from triglycerides and phospholipids. Free fatty acids are measured by a
titration method (AOAGI1995) and are expressed as a percentage. In
fish oils used in fish feeds, the usual upper limit for fatty acids is 3%.
b.2. Oxidative Rancidity:
Oxidative rancidity is caused by the reaction of a free radical with
double bonds of unsaturated fatty acids. Oxidative rancidity is measured
by detected and quantifying aldehydes and ketones or by measuring the
final products of oxidation. The levels of intermediates products of lipid
oxidation rise in the early stages of oxidation, then fall in the late stages.
D. Biological Evaluation Method:
a) Instantaneous growth rate ( Gw )
b) Digestibility
c) Protein Efficiency Ratio (PER)
d) Biological Value
e) Feed Conversion Ratio (PCR)
f) Net Protein Utilization (NPU)

6. a) Instantaneous growth rate (Gw):
Growth: Over a specific time period, growth of groups of fish fed various
experimental diets is calculated and compared.
Daily Instantaneous growth rate (Gw):
➢ This value can be used to compare growth as daily basis
Gw =
ln W1−ln W0
𝑇
Where,
W1 = Wt. at the end of the study
W0= Wt. at the starting of the end
T= time interval in days
➢ To convert daily instantaneous growth rate to percentage following
formula is used
% W/day = (𝑒𝐺𝑤
-1)×100
b) Digestibility:
This method is useful both with feed ingredients and with finished feed.
An inert material, Chromic Oxide (𝐶𝑟2𝑂4) is added to the feed at a level of
0.5-1.0%. The test fishes fed for several days then faces are collected and
Cromic Oxide level both in feed and faces are determined.
Digestibility Co-efficient:
Digestibility for feed:
Dig. Co-eff. = 1 −
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑒𝑒𝑑
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
For ingredients:
Dig. Co-eff. = 1 −
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑒𝑒𝑑
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
×
% 𝑜𝑓 𝑛𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑙𝑒𝑣𝑒𝑙 𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
% 𝑜𝑓 𝑛𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑙𝑒𝑣𝑒𝑙 𝑖𝑛 𝑓𝑒𝑒𝑑

7. Smith and Lovell (1973) given equation is:
% Dig. = 100-
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑒𝑒𝑑
%𝐶𝑟2𝑂4 𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
×
𝑝𝑟𝑜𝑡𝑒𝑖𝑛𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
𝑝𝑟𝑜𝑡𝑒𝑖𝑛𝑖𝑛 𝑓𝑒𝑒𝑑
Gross digestibility:
Gross % dig. =
𝑁𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑖𝑛 𝑡𝑎𝑘𝑒 –𝑁𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑖𝑛 𝑓𝑎𝑐𝑒𝑠
𝑁𝑢𝑡𝑟𝑖𝑒𝑛𝑡 𝑖𝑛 𝑡𝑎𝑘𝑒
×100
But concerning metabolic product (nitrogen basis)
% digestibility =
𝐼𝑛𝑡𝑎𝑘𝑒 𝑁−(𝑓𝑎𝑐𝑒𝑠 𝑁−𝑚𝑒𝑡𝑎𝑏𝑜𝑙𝑖𝑐 𝑁)
𝐼𝑛𝑡𝑎𝑘𝑒 𝑛
×100
c) Protein Efficiency Ratio (PER):
PER means weight of cultured species gained per unit of protein fed
PER =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑔𝑎𝑖𝑛 (𝑔)
𝑝𝑟𝑜𝑡𝑒𝑖𝑛 𝑓𝑒𝑒𝑑 (𝑔)
d) Biological value:
Biological Value means the percent of protein utilization in the body excluding
metabolic protein.
Apparent BV =
𝐹𝑜𝑜𝑑 𝑁−( 𝑓𝑒𝑐𝑎𝑙 𝑁+𝑢𝑟𝑖𝑛𝑎𝑟𝑦 𝑁+𝑏𝑟𝑎𝑛𝑐ℎ𝑖𝑎𝑙 𝑁)
𝐹𝑜𝑜𝑑 𝑁
×100
e) Feed Conversion Ratio (FCR):
The effectiveness of compound is usually expressed in terms of FCR. It is also
known as feed efficiency or food conversion ratio.
It is the amount of food necessary to produce 1 unit weight of animal.
FCR =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡𝑜𝑡𝑎𝑙 𝑢𝑠𝑒𝑑 𝑓𝑜𝑜𝑑 (𝐾𝑔)
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡𝑜𝑡𝑎𝑙 𝑎𝑛𝑖𝑚𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑(𝑘𝑔)
For example, if 1250 kgs of shrimp were produced from a pond which
2000kgs of pellets feed had been used during the growing cycle,

8. The FCR would be-
FCR = 2000/1250 =1.6
Usually, the FCR written as 1.6:1, it means 1.6 kg feed is necessary to produce
1 kg shrimp.
Lower the FCR is better. Because, less feed is require per weight gained.
e) Net Protein Utilization (NPU):
f) NPU means per unit proteins absorbed by the fish.
Apparent NPU =
𝑃𝑟𝑜𝑡𝑒𝑖𝑛 𝑐𝑜𝑛𝑡.(𝑔)𝑒𝑛𝑑 𝑜𝑓 𝑒𝑥𝑝.−𝑃𝑟𝑜𝑡𝑒𝑖𝑛 𝑐𝑜𝑛𝑡.(𝑔)𝑜𝑓 𝑓𝑖𝑠ℎ 𝑎𝑡 𝑠𝑡𝑎𝑟𝑡 𝑜𝑓 𝑒𝑥𝑝.
𝑑𝑟𝑦 𝑝𝑟𝑜𝑡𝑒𝑖𝑛 𝑓𝑒𝑑 (𝑔)×𝑃𝑟𝑜𝑡𝑒𝑖𝑛 𝑑𝑖𝑔𝑒𝑠𝑡𝑖𝑏𝑖𝑙𝑖𝑡𝑦 𝑐𝑜−𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡
E. Microbiological Standards:
Several researchers have measured total aerobic bacterial counts and the
range of bacterial species present in commercial fish feeds. Trust (1971)
and Trust and Money (1972) reported total colony forming unit (cfu)
ranging from 103
to 109
cfu/g in commercial fish feeds. Kitao and Aoki
(1976) found levels of 102
to 105
cfu/g in Japanese fish feeds.
Common species of microbes are-
➢ Aeromonas hydrophilic
➢ Clostridium perfringers
➢ Pseudomonas
➢ Staphylococcus
➢ Streptococcus
➢ Salmonella
F. Economic Evaluation:
Ideally, feed formulation and diet evaluation should be based on
production i.e. least cost per unit of produced. Also one must examine the
cost of feed per unit of product sold to truly understand the contribution of

9. feed per unit of fish production. This is must be done in the context of feed
type and fish life history stage, taking into consideration the quantity of
feed used at each stage and the benefit of using superior feed in the early
stage of rearing compared to the relative cost.
Conclusion:
Proper health of fishes of the intensive and semi-intensive culture almost
completely depends on good quality feed. Evaluation of fish feed is
essential for maintaining quality of feed. There are differences in the
physical and chemical characteristics among commercial fish feeds. Pellet
floatability, dust percentage, water physical integrity and fish weight can
be applied by the fish farmer to evaluate commercial fish feed quality
References:
Halver John. E, 2000. 3𝑟𝑑
Edition, Academic Press, Landon.
Lovell, R. T. 1981. Fish feed analysis and fish nutrition studies. Auburn
University, Alabama, USA. 65p.