Drying sessions were conducted across Nigeria to study the interaction between fish weight loss and the meteorological parameters. Correlation analyses using weight loss values show that latitude is strongly related (r =+0.96) to weight loss of fish inside the dryer while altitude had a weak relationship (r = +0.24) with weight loss. The results show that New Bussa recorded more weight loss of fish than Jos, despite their uniform latitude. Weight loss records in Jos, was however better than those of Warri and Ibadan

Adenike Ibitoye

Emeka Ugoala

Julius Olokor

English

Nature Precedings

STUDY OF FISH WEIGHT LOSS IN SOLAR DRYER ACROSS 
DIFFERENT AGRO-ECOLOGICAL ZONES OF NIGERIA 
 
By 
OLOKOR, J.O.; UGOALA, C AND IBITOYE, A 
FISHERIES TECHNOLOGY DIVISION,  
NATIONAL INSTITUTE FOR FRESHWATER FISHERIES RESEARCH (NIFFR), P.M.B 6006 
NEW BUSSA, NIGER STATE, NIGERIA 
 
 
ABSTRACT 
Drying sessions were conducted across Nigeria to study the interaction between fish 
weight loss and the meteorological parameters. Correlation analyses using weight loss 
values show that latitude is strongly related (r =+0.96) to weight loss of fish inside the 
dryer while altitude had a weak relationship (r = +0.24) with weight loss. The results 
show that New Bussa recorded more weight loss of fish than Jos, despite their uniform 
latitude.  Weight loss records in Jos, was however better than those of Warri and Ibadan.  
  
KEYWORDS: Meteorological; Drying; Weight loss; Solar dryer; Correlation 
 
INTRODUCTION 
The relative high moisture content and high degree of unsaturated fatty acids in fish 
accounts for its perishability either during processing or storage. Recent developments in 
fish preservation suggest that dynamic aspects of fish systems rather than equilibrium 
properties could be very crucial in extending the shelf life of processed fish. 
 
Basically, in tackling the problems of post harvest losses in the developing economies, 
the role of the fish scientist would mean exploring means  to maximizing yields, assure 
safety and ultimately to transfer product technology from one country to another. There is 
much potential for the study of fermentation processes, mechanics of smoking as well as 
frying to develop quality products in a friendly environment. Equally, it is increasingly 
important to understand the basic interactions between the deteriorative processes, the 
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products formed in these processes, and the effects of external factors influencing these 
processes. This will also provide a firm basis for the technology, and identify critical 
points at which greater success may be achieved in controlling quality deterioration and 
functional properties in order to provide a firmer basis for predictive methods of quality 
deterioration. 
Fish preservation requires both basic and adaptive research. In sun-drying, energy is used 
to evaporate the water.  The main sources of energy are solar energy, used either directly 
as in sun-drying, or indirectly as in crib drying; and energy derived from burning material 
such as wood, coal, gas or oil. In all cases, except direct sun-drying, the energy is 
transferred to air (the temperature of which is thus increased), and thereafter to the fish 
where it evaporates the water and is itself cooled.  
During the day ambient air increases in temperature as a direct result of the sun's heating 
effect. The air stores the sun's energy which can then be used to dry fish during the day. 
During the middle hours of the day, the air temperature is raised but relative humidity is 
also reduced allowing air to have an increased capacity for drying through its increased 
temperature, and therefore more energy available for evaporation.  
The drying of food is the world's oldest known preservation method, and dried fish has a 
storage life of several years. The method is cheap, the work can be done by the fisherman 
and family, and the resulting product is easily transported to market. 
As has already been acknowledged by previous studies such as those of Trim and Curran 
(1983), Doe et al. (1977), Doe (1998), Jason (1988), and Eyo (2001),  the primary 
principles behind the sun drying of fish using traditional open sun methods or solar dryers 
are meteorological. Thus, it requires a proper understanding of the working of these 
principles to obtain better and faster drying. The physics behind the natural drying of fish 
is the interplay of temperature, relative humidity, sunshine duration, and radiation and 
wind speed. Previous studies took these parameters into consideration while calculating 
drying rates. Attempt is made in this study to correlate all these parameters and see their 
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individual impact on the rate of fish drying using fish weight loss data from the Kainji 
Solar Dryer.  
 
MATERIALS AND METHODS 
Data for this study were collected from drying sites in New bussa, Baga, Jos, Ibadan, and 
Warri using a 50kg top loading casella weighing balance, thermometer, hygrometre, 
windvane,cup anemometer and photometre. The meteorological data were collected in 
March and August of 1999 and 2000, period of dry and wet season respectively. The data 
were collected at different times as shown in table 1. 
 
A suitable site in each zone was chosen based on exposure to sunlight. The solar dryer 
made up of sticks, fish drying rack all covered by a transparent polyethylene sheet is set 
up before sunrise. The fresh fish to be dried were gutted from the dorsal part, washed, 
salted and spread on the rack inside tent. Weight loss data was obtained by deducting 
final weight from initial weight. 
 
RESULTS 
Table 1: Meteorological data obtained near drying site and Percentage weight loss of fish 
inside solar dryer in March and August 1999 and 2000   
Days 
3-day 
intervals 
Weight 
loss 
% 
Temperature 
    oC 
Relative 
Humidity 
   % 
Sunshine 
duration 
Hours 
Radiation 
Cal/cm2 
 
Wind speed 
Km/hour 
15/03/20 57.4 38.1 24.5 6.6 7.27 11 
18/03/20 60.1 38.1 20.8 6.8 7.21 10.8 
21/03/20 52.8 37 29 6.9 6.95 11.2 
9/08/20 38.1 31 68.8 4.4 5.1 6.5 
14/08/20 35.5 31.8 68 3 5.1 7.1 
19/08/20 38.7 32 75.5 4.1 5.3 6.8 
3/03/99 51.2 36.8 24.8 7.3 6.86 10.2 
6/03/99 58.2 36.8 21.5 7.6 6.88 12.1 
9/03/99 50.1 36.8 32.1 6.7 6.29 12.4 
12/08/99 36.3 31.8 67.8 4.1 5.22 6.6 
17/08/99 37.1 28.3 71 4.1 5.01 6.1 
22/08/99 38.2 30.8 77.1 4.4 5.81 7.3 
Initial weight of fish was 100g approximately 
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WEIGHT LOSS OF FISH IN SOME TOWNS OF NIGERIA
0
5
10
15
20
25
30
35
40
WARRI IBADAN N/BUSSA JOS BAGA
TOWN
%
W
EI
G
H
T 
LO
SS
Series1
Series2
Series3
 
Figure 2: Weight loss of fish in some towns of Nigeria 
 
 
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Figure 4.7: Relationship between weight loss, Sunshine, Radiation and Windspeed.
0
1
2
3
4
5
6
7
8
15
/03
/02
18
/03
/02
21
/03
/02
08
/09
/20
02
14
/08
/02
19
/08
/02
03
/03
/19
99
03
/06
/19
99
03
/09
/19
99
08
/12
/19
99
17
/8/
19
99
22
/08
/19
99
Days
W
ei
gh
t l
os
s 
(g
m
s1
0 )
0
2
4
6
8
10
12
14
S
un
sh
in
e 
(h
rs
), 
R
ad
ia
tio
n 
(c
al
/c
m
2 )
, W
in
ds
pe
ed
 (K
m
/h
r)
weight loss Sunshine
Radiation Windspeed
 
 
 
 
Table 2: Correlation coefficients between weight loss and meteorological parameters 
  Temperature Rel. Humidity Sunshine Radiation Wind speed 
Weight loss R= +0.944 r= -0.974 r=+0.944 r=+0.970 r=+0.945 
 
 
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Figure 4.8 Hourly fluctuation in weight loss and metrological parameters affecting fish drying
0
10
20
30
40
50
8am 10am 12pm 2pm 4pm 6pm
Time of day
W
ei
gh
t l
os
s 
(g
m
s)
, T
em
p 
(0
c)
, R
. h
um
id
ity
 (%
)
-0.2
0.5
1.2
1.9
2.6
3.3
4
S
S
 (H
ou
rs
) R
ad
ia
tio
n 
(c
al
/c
am
2 )
 W
in
d 
(K
m
/h
)
Weight loss Temp
RH SS
Rad Wind
 
DISCUSSION 
 Impact of Meteorological parameters on Weight Loss of Fish 
Table 1 shows meteorological data collected during the period of fish drying trials in 
1999 and 2000. These are shown against weight loss of fish in the solar dryer for the 
given day. The interaction between weight loss and the meteorological parameters are 
clearly shown in Figures 1 and 2. Figure 2 shows weight loss of fish rising and falling 
along with prevailing meteorological parameters from one season to another. It can be 
seen that, in March and August 1999 and 2000 meteorological parameters obtained 
outside the solar dryer were consistent with weight loss of fish inside the dryer. The line 
graph shows that weight loss pattern follow variability in the meteorological parameters.  
 
Figure 2 is a typical hourly pattern of meteorological parameters obtained at the drying 
site within a day. It shows that fish weight loss varies not only within seasons but also 
within the day. The extractive forces of the solar dryer are stronger by mid-day to late 
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afternoons. This time was observed on the field as the period when weight loss is highest. 
Figure 2 shows weight loss increasing from 8am to a peak between 2-4pm when 
radiation, sunshine and temperature are highest and relative humidity lowest. Correlation 
analyses (Table 2) show that relative humidity had the highest relationship though inverse 
(r=-0.974) followed by radiation (r=0.970). The least, but still strong, is temperature 
(r=0.944). This shows that meteorological parameters are the primary determinants for 
fish drying either in the open sun or within the solar dryer, since weight loss during 
drying follow the pattern of these parameters 
 
Pilot Trial of Solar Dryer in Eco-Zones of Nigeria 
Weight Loss of fish inside solar Dryer 
Figure 1 shows weight loss of fish inside solar dryer in five Eco-zones of Nigeria during 
a pilot trial. The table shows that at the end of three days drying, weight loss of fish was 
lowest in Warri, (Forest Belt, latitude 5o 30´N), with a total of 204gm or 27.6%. This is 
followed by Ibadan (Wooded Savanna, latitude 7 o 22´N) with a total weight loss of 
329.5gm or 44%. Fishes dried in the solar dryer in Jos (Sudan Sahel, latitude 9o 55´N) 
recorded a total weight loss of 411gm or 56%. New Bussa (Guinea Sudan, latitude 9 o 
51´N) was next with a total weight loss of 450.5gm or 60% while in Baga north of 
Maiduguri (Sahel, Latitude 13o 10´N) total weight loss was 514.3gm or 63%.  
 
Weight loss decreased as latitude increased from the south to the extreme north of 
Nigeria, except for Jos due to lower ambient temperature. This is in accordance with the 
results of previous studies showing a strong correlation between latitude and radiation. 
The correlation between latitude and global radiation for instance was put at r = +0.80 
(Kowal and Knabbe, 1972; Udo and Aro, 1999).  
 
Correlation analyses using weight loss values from Table 2 show that latitude is strongly 
related (r =+0.96) to weight loss of fish inside the dryer while altitude had a weak 
relationship (r = +0.24) with weight loss. The table shows that New Bussa (Latitude 9 
o.510N) with an altitude of 180m recorded more weight loss of fish than Jos (Latitude 9o 
53´N) with an altitude of 1275m. This is likely due to cooler climate resulting from high 
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altitude and frequent cloud cover experienced during the trial period in Jos. Despite its 
altitude, weight loss records in Jos, was better than those of Warri and Ibadan.  
 
 
CONCLUSION 
Processing could bring about the state of thermodynamic metastability in processed fish. At 
high humidity, dried fish flesh may absorb moisture from the air until equilibrium is reached. 
However, relative humidity influenced the weight loss of fish during drying as well as 
radiation and temperature. Across the different agro-ecological zones of Nigeria, fish weight 
loss was observed to be highest in the Northeast (63%) but was lowest in the South south 
(27%). Drying fish to a moisture content sufficient to inhibit the growth of xerophilic moulds 
and insects may not be feasible for commercial storage and may be unacceptable to 
consumers. 
 
 
REFERENCE: 
Doe, P.E. (1998) Fish drying and Smoking, Production and Quality, P.E. Doe 
(ed), Technocomic Publishing Co., Inc.: 851New Holland Ave. Box 3535 
Lancaster PA. 17604 USA. ISSBN: 1533766680. 400pp. 
Doe, P.E. Ahmed, M,  Muslemuddin, and  Sachithanathan, K  (1977 ) A 
polyethylene tent Dryer for improved Sun drying of fish , Food technology 
in Australia, 29, 437 – 441  
Eyo, A.A. (2001) Fish Processing Technology in the Tropics. UNILORIN Press. Pp 
130-152 
Jason, A.C (1988). A Study of Evaporation and Diffusion Process in the Drying of 
Fish Muscle. In: Foundamental Aspects of Dehydration of Foodstuffs. 
Society of Chemical industry of London. Macmillian, New York. Pp103-135 
Kowal, J.M and and Knabbe, D.T (1972). An Agroclimatological Atlas of Northern 
States of Nigeria with Explanatory Notes. Zaria Pp 14-26.      
Trim, D. S. and C. A. Curran (1983). A comparative study of solar and sundrying 
of fish in Ecuador Tropical Product Institute 56 / 62 Gray`s  inn Road. 
London. Pp 11 - 17. 
Udo, S.O and Aro, T.O (1999) Technical Note Measurement of global 
Photosynthetically-active and downward infrared radiations at Ilorin, 
Nigeria. Renewable Energy; Vol. 17n no 1. pp113-122  
 
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A comparative study of solar and sundrying of fish

A polyethylene tent Dryer for improved Sun drying of fish ,

Fish drying and Smoking, Production

Society of Chemical industry of London. Macmillian,

Technical Note Measurement of global Photosynthetically-active and downward infrared radiations at Ilorin, Nigeria. Renewable Energy; Vol. 17n no 1. pp113-122 N a t u r e P r e c e d i n g s : d o i : . / n p r e

Study of Fish Weight Loss in Solar Dryer Across Different Agro-Ecological Zones of Nigeria

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Study of Fish Weight Loss in Solar Dryer Across Different Agro-Ecological Zones of Nigeria

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