ArticlePDF Available

Natural food for Nile tilapia (Oreochromis niloticus L.) in the Rumaitha river north of Muthanna province, southern Iraq


Abstract and Figures

Natural food for Nile tilapia
Content may be subject to copyright.
Kareem Z. Negaud1, Taha Y. Al-Kafaji2 and AbdAlkareem J. Abu Al-Heni3
1Department of Animal Production, College of Agriculture, Al-Muthanna University, Iraq.
2Sawa Lake Center, Al-Muthanna University, Iraq.
3Department of Agricultural Research, Animal Resources and Fisheries Center, Science and Technology Ministry, Iraq.
The present study aimed to provide information on the natural food of the Nile tilapia (Oreochromis niloticus) in the
Rumaitha river on north of Muthanna city, 97 samples were collected with monthly hunting campaigns from July 2017 to June
2018 by using electric fishing, the total length ranged from 4.5 to 26 cm, while the total weight ranged 1.6 to 401.1 g. Analysis
was done by using frequency of occurrence (O), point methods(P) and important ranking index (R%), It was found that tilapia
tilted Omnivorous with its great tendency to eatingthe plant components, which accounted for 78.52% of the food consumed
and that organic matter the most preferred component and 38.74% followed by algae and then plants and their tissues, while
the proportion of animal origin components 18.14, the zooplankton were the most preferred component, with 8.31% followed
by un examined food component, insects and their larvae. It was found that the fish was highly feeding activity with 91.25%
and the feeding intensity was 23.06 degrees/fish.
Key words : Natural food, Nile Tilapia, Al-Rumaitha river, Iraq.
Plant Archives Vol. 19 No. 1, 2019 pp. 460-464 ISSN 0972-5210
Fish and aquaculture are an important food source
for the individual eit her as an ingredients in the
manufactu r e processes of other animal feed, th e
important of fish returns to their bodies which contain a
high rate from protein, unsaturated fatty acids lipids and
other nutrients as vitamins, calcium, phosphor and iron
(Al-Eze and Abdul Khaliq, 2002). The knowledge of fish
biological aspects is necessary to the to improving the
fish wealth, and any step to developingthis wealth is futile
if it does not includingthe sufficient knowledge of different
aspects of lifeand the most important about its are studies
on nutrition (Al-Rubaye, 1989). Tilapia is the common
name which is called to thegroup of fish within Cichlidae
which contain 1524 species (Eli, 2005) which are under
three main species as Oreoch romis, Sarotherodon,
Tilapia (Popma and Masser, 1999). It is one of the
intruderspecies on the Iraqi rivers and water bodies and
is currently existing insome of the Iraqi southern cities
(Ghazwan, 2016). This fish speared in the southern
marshes of Iraq and it began dominated in other local
fishes and negatively affected on its reproduction in the
southern cities (Scientific Symposium, 2012). The first
presence of Grass tilapia, Tilapia zilli was recorded by
Salih (2007) in Euphrates river at Al-Musayyib city in the
middle of Iraq, the first presence of O. aureus was
recorded by Al-Mutlaq and Faisal (2009) in the southern
part of the main outfall in Al-Basrah city, AL-Zaidy (2013)
also recorded the first presence of tilapia Tilapia zilli in
the Al-Delmj marsh at the middle of Iraq, Abulheni and
Abbas (2017) also recorded the presence of two species
of tilapia O. niioticus and O. aureus in the Euphrates
river at Al-Hindyah barrier, Tilapia fish is an omnivorous
fish according to Surrounding condition, it basically feeds
on algae and other plant substances as well as detritus
that make it the link between the higher nutrition levels
and the lower in the food chain in the water, also its feeding
depending in small insects and parts of fishes (Turker et
Natural Food for Nile Tilapia 461
al., 2003) and it plays an important role as filtersthrough
their ability to filter food by picking up the food particles
in the water column. Also, it changes its diet as a result
of environmental changes, especially pollution,the types
and sizes of consumed food is changed with size and age
of fish, the fish eating the food that is suitable with it
mouth size and the capacity of intestine and the increasing
of fish age make the digestive system becomes more
sophisticated besides the increase in length of intestine
which making fish able to digestion the most complication
food typ es which cannot be diges ted at an early
age(Benavides et al., 1994). There is a huge of small
fish tended to eat zooplankton, which can be digested
easily as comparing with phytoplankton and other plant
parts as well as it needed to foods with high protein
ratiobecause of the high growth rate and highly metabolic
processes. the importance of fish feedingis necessary to
study the massive needed for it as a source forenergy,
growth,and survival alive at the first time of fish life’s,
which is the main source for food is the yolk sac, however,
the need for larger quantities to be supplied from the
external environment soon arises. The studies about the
populationto fish of Cichlidae especially, which was
recorded its pres ence in Iraq did not receive much
attention therefore, the present study aims to study the
components of natural food, nutritional habits and
nutritional efficiency of Nile tilapia in the Rumaitha river
in the north of Muthanna city.
Materials and Methods
Study region
Euphrates river is the longest rivers in Asia and It is
ranked 24th in the world (Whitton, 1975) the total length
of it from the upstream until when it meeting Tigris river
at the Qurnaattained 2940 Km, 1159 from it flows in Iraqi
lands, Euphrates river is branching at the beginning of
Al- Hindyah barrier into two main branches ShattAlhilla
and ShattAl-Hindyah, ShattAlhilla flows south which it
passing Alhilla and Al Diwaniyah cities and almost
disappear in the agricultural lands south of Rumaytha
(Ministry of Water Resources, personal contact), the
length of Al-Rumaitha river starting from entering the
administrative borders of the region until it faded In the
outskirts of Al-Rumaitha district attained about 36.60 Km
and the yearling rate of the river drainage attained 14.4
M3\Secon d (Th e Dir ectorat e of Water Resour ces,
personal contact). The surface of area which Al-Rumaitha
river flow on it tends to general level that leads to the
slow flow of wat er which was the reas on for the
increased concentration of pollutants and weakening the
ability of the river to self-purification as well as increasing
the percentage of water leaks into soil and ground water,
the sediments of t he r iver are cha r acterized as
heterogeneous and consisting of clay, silt and sand a
station on the Al-Rumaitha river was chosen within the
coordinates 31°31’35.8" N 45°11’20.2" E for the samples
collection, the width of the river at the study region amount
to (30-35 M) and the depth (3-5 M). There are many
aquatic plants in the study region as Reeds Phragmites
australis, Ceratophyllum Ceratophyllum demersum and
Typha Typha domenyenasis (Mohamed and Al-Jubouri,
2017) and UtriculariaPotamogeton pectinatus (Al-
Amari, 2011). Different natural plant appears along the
ri ver and it s branches as Willow, Tama risk and
Populousas well as other plants which randomly
distributed (Al-Abadi, 2017), whereas the important fish
which existing in study region as Aspius vorax, Planiliza
abu, Silurus triostegus, Mesopotamichthys sharpyei,
Alburnus caeruleus, Cyprinus carpio, Carasobarbus
lutues and Carassius auratus (Al-Daham, 1977) as well
as all three species of tilapia fish O. niloticus, O. aureus
and Coptodon zilli (Trewevas, 1983; FAO, 2012).
Field and laboratory work
The samples of fish were collected monthly from
July 2017 to June 2018, by using electric fishing and fishing
effort was limited by one hour per month. Fish were placed
in ice-cored containers in the summer months and storage
frozen until measurements of life were made, the fish
were classified according to (FAO, 2012; Trewavas,
1983), the frozen fish were washed by water to remove
the ice then they dried and the total length was measured
close to 1mm by using a wooden ruler , the measurement
was recorded by using the digital vernier. fish were
weighted closed to 0.1 gm, then the fish was dissection
from the abdominal region and the gut was extracted
and the third front of gut was cutting to representing the
stomach (Al-Shammaa, 1993) and samples were placed
in small containers that recorded on it the information
each fish. The contents were emptied in a glass dish and
examined under the dis s ectin g microscopea t x4 0
magnification and the microscope under the magnification
x 450 to identify on the food components in the gut, the
food elements was diagnosed according to (Edmondson,
1966). Two methods were used to analyze the content of
the gut as the point method and occurrence method
according to Hyslop (1980) and important Ranking Index
(IRI) was calculated to each food component through
equation :
R = (O%P%/P%×O%)×100 (Stergiou, 1988).
The fullness degree of the stomach was recorded by
visual observation (Sinha and Jones, 1967) and gave the
462 Kareem Z. Negaud et al.
points 0, 5, 10, 15, 20, 30 depending on the fullness degree
as (empty, rare ¼full, 2/1 full, 4/3 full, full) sequentially
according to feeding activity by using the equation :
Feeding activity % =
The number of feeding fish
____________________________________________ × 100
The total number of examined fish
(Gordan, 1977) and the feeding intensity by using the
equation :
The feeding intensity(Degree\Fish) =
The total scores obtained from the fullness index
______________________ _____________________ _______________________ ________
The number of feeding fish
(Dipper et al., 1977). Statistica l Package of Social
Science (SPSS) was used for the statistical analysis and
finding the correlation values and comparing between
means (Al-Aqili and Al-Shayeb, 1988) and the differences
were examined according to Duncan test (Duncan, 1955).
Results and Discussion
The food components according to length groups
The fish was divided into two longitudinal groups ,
the more than 12 cm and the less than 12 cm (table 1),
the result of the statistical analysis showed there was
significant differences in the feeding of the longitudinal
groups on the algae and the zooplankton and there was
no significant differences in the feeding of longitudinal
groups on other food components and when we examined
the gut components of the fish with a length less than 12
cm, Algae was ranked first in the points method (P) and
occurrence method (O) moreover important ranking index
(R), Algae accounted 35.69% for the (R), 19.07% for
the (O) and 29.04% for the (P), whereas ranked second
18.42%, 25.90%, 30.73 by the three methods sequentially
whilst the ratios of zooplankton were 13.15%, 15.17%,
12.85% sequentially, the other components and its tissues
according to (R) were accounted %8.6 ,unexamined food
substances 7.47%, Diatoms 1.92 and insect and its larvae
The high percentage of algae in the longitudinal groups
less than 12 cm may be its return to easier digest by fish
than other aquatic plants (Almukhtar, 1982), which is
proportional with the age of fish and the development
degree of fish digestive system (Benavides et al., 1994),
small fish also avoid diatoms that have a hard wall that is
hard to digest as compared with algae (Otieno et al.,
2014) and this explained the low ratio of diatoms in the
food of small fish, whilst the detritus in the longitudinal
group fish more than 12 cm was ranked first by three
methods and the ratio of (R) theratio of it was about half
of the amount of food intake attained 46.72% followed
by algae by 13.84% the plants and their tissues occupied
third with ratio 11.50% and the insects and larvae were
recorded 1.67%. It is noted decreasing the ratio of micro
size food components as zooplankton and increasing the
ratio of complicated structure component with large parts
as plants and their tissues ,the reason may be due to the
increasing the development of the digestivesystem, as
well as increasing of sand granules in big size fish as
compared with small size fish ,which supporting this
opinion its help in the digestion processes as Al-Mukhtar
(1982) pointed there is a positive relationship between
the size of the prey and the length of fish generally .the
results of this study differed with the results of Khalifa
(2017), who pointed that the detritus ranked first at ratio
61.62% and the algae occupied 11.13% and its ranked
second from the importance to Nile tilapia fish at Tigris
river southern Baghdad , the result agreed with Abulheni
et al. (2017), as for detritus it ranked first to fish group
more than 15 cm by (R) at ratio 46.85% and it differed
with the results by the first occupied by the component
itself in the juvenile food and in the recordingof the
mollusks presence in the little ratio in the content of Gut
in the two longitudinal groups and by all using methods,
whereas not recorded any presence of it in the results of
current study, the table 2 showed that the Nile tilapia in
Al-Rumaitha river was Omnivorus with their tendency
to eating the plant components, which recorded in the
fish group less than 12 cm ata ratio 76.94% and the animal
component 21.84% whereas it ratios in the fish with length
more than 12 cm 80.03% and 14.47% for the plant and
animals components sequentially, the consumption of small
fish of animal components at higher rates than big fish is
due to the needing of the body in the initial stages of
growth to foods with high content of energy and protein.
These requirements are available in the animal origin foods
(Benavides et al.,1994). This result agreed with Abulheni
et al. (2017), this species of fish is anomnivorous with a
preference to eating the plant components with it a large
and small sizes generally, the ratio of plant components
in the small length groups 82.46% and the animal
components 517.53%, whereas it ratio in the big length
group 82.32% and 17.64% to the plant and animal
components sequentially.
The general food components
Table 3 showed that the detritus and algae ranked
first and second in an importance index which formed
34.74% and 24.77% sequentially, the plants and their
tissues ranked third 10.05% and the zooplankton 8.31%
followed by unexamined food substances at a very close
rate attained 8.24% then the diatoms which formed about
Natural Food for Nile Tilapia 463
4.96%, insects and larvae ranked last attained 1.59%, in
many studies Nile tilapia classified as a herbivorous and
several researchers agree that despite the diversity of it
feeding include fish, insects, etc. but the plant components
still contribute the largest compenont in its food (Otieno
et al., 2014), the results of the study agreed with what
was found by Khalifa (2017), who pointed that the highest
percentage of this fish food is detritus 61.79%, followed
by algae 10.22% and plants and their tissues (9.13%).
the difference in the ratios of food components between
study and other or between site and other maybe return
to the effect of environmental fact ors and the food
abundance, as well as the dominance of the food
component to anotherwas the result of selective feeding
on different types of fish depending on the nutritional
benefit or maybe these differences resulted from the
dominance of the component on other in the water body
(Canonico et al., 2005). Table 3 showed the tilapia fish
has a high nutritional activity attained 91.25% and a
feeding intensit y att ained 23.0 6 degrees/fish. The
increasing therate of feeding activity may be due to the
efficiency of the used fishing equipment, the using of gill
nets leads to return part of the food from the stomach
while it trying to escape from the nets or may be due to
the feeding habitat which it depending on it this species
also it enables the fish to take available advantage of the
food groups in the environment which lives on itas well
as it considered asravenous fish fed continuously if food
available (Shola et al., 2017). This result agreed with
Abulheni et al. (2017), who pointed that the Nile tilapia
fish in the Euphrates river, Al-Musayyib at highly feeding
activity on throughout the year attained 97.43% and
feeding intensity attained 23.28 degree\fish this result
agreed with Khalifa (2017) result who recorded the higher
feeding activity of Nile tilapia in Tigris river attained %100
and the lowest feeding activity for it was recorded at
winter season attained 83.00%.
Abolheni, A. A. J., T. S. Husain, A. A. M. Ruhaij, H. F. Shaker
and S. M. Hasan (2017). The Overlap among Three Types
of Tilapia in Euphrates River. Journal of Tikrit University
For Agriculture Sciences. Special Issue : 509-516p.
Table 1 : The percentages of the natural food components of the two longitudinal groups of Nile tilapia in the Rumaitha river are
calculated by the points (P), The occurrence (O) and The Important Ranking Index (R) methods.
Length more than 12 cm Length less than 12 cm
Food components X2
O % P % R % O % P % R %
Plants and their tissues 10.82 15.45 11.5 12.5 10.69 8.6 0.4 ns
Insects and larvae 4.76 5.1 1.67 5.92 4 1.52 0 ns
Algae 13.41 15 13.84 19.07 29.04 35.69 9.6*
Diatoms 15.15 7.68 8 11.18 2.67 1.92 3.6 ns
Detritus 19.48 34.92 46.72 18.42 25.9 30.73 3.2 ns
Sand and Clay granules 12.55 6.27 5.41 8.55 2.12 1.16 2.66 ns
Un examined food substances 12.12 10.83 9.02 11.18 10.37 7.47 0.25 ns
Zooplankton 11.68 4.72 3.78 13.15 15.17 12.85 4.7*
*Referred to significant differences at probability level (0.05), N.S referred to no significant differences at probability level.(0.05).
Table 2 : Feeding habitat of Nile tilapia fish according to
Important Ranking Index (R) in Rumaitha river during
studying period.
Food components
Length group
Animal % Plant%
Less than 12 cm 21.84 76.94
More than 12 cm 14.47 80.03
General 18.14 78.52
Table 3 : The percentage of Gut contents from natural food
which c a lculated b y th e p oint s met h od (P) ,
occurrence method (O), the Important Ranking Index
(R), activity and feeding intensity of Nile tilapia fish
which caught in Al-Rumaitha river during studying
Examined method%
Food components
Plants and their tissues 11.66 13.07 10.05
Insects and larvae 5.34 4.55 1.59
Algae 16.24 22.02 24.77
Diatoms 13.16 5.17 4.96
Detritus 18.95 30.41 38.74
Sand and Clay granules 10.55 4.19 3.28
Unexamined food substances 11.65 10.60 8.24
Zooplankton 12.41 9.94 8.31
The number of examined fish 80
The number of feeding fish 73
Total points 1684
Feeding activity %91.25
Feeding intensity 23.06-degree \ fish
Abulheni, J. A. and L. M. Abbas (2017). First record of the
Tilapia Oreo c h romis nilo t i cus (Linnae us, 17 5 8 ) in
Euphrates River at Al-Hi ndiaBarr abe Middle of Iraq.
Journal of the University of Kerbala. Speciel Tissue: 18-
Al-Abadi, A. A. K. (2017). Spatial analysis to the quality of Al-
Rumaitha river. MSc. Thesis. Arts college \ Al-Qadisiyah
University, 145p.
Al-A mari, M. J. Y. (20 11). Stud y of some biolog ical and
environmental aspects of fish community in Alhilla river \
Iraq. Ph. D. thesis. College of Science, Babylon University,
Al-Daham, N. Q. (1977). Fish of Iraq and Arab gulf. part I.
Alarshad press-Baghdad.546p.
Al-Eaqili, S. A. and S. M. Al-Shayeb (1988). Statistical analysis
by using the SPSS.Da r_ElS horou k for publishing and
distribution. Jordan, Amman. 288 p.
Al-Ezzi, J. M. H. and A. A. A. Abdul Khaliq (2002). The openness
of Investment on fish projects and rates of outputs which
achieved from it. Iraqi Journal of Agriculture Ssciences,
33(1) : 175-182p.
Al-Mukhtar, M. A. H. (1982). Study biology of two species of
fresh water fishes Barbus luteus (Heckel) and Aspius vorax
(Heckel) in Al-Hammar marsh – Al-Basrah. PhD thesis
.agriculture college – Al-Basrahuniversity ,270p.
Al-Rubaie, R. K. (1989). Study of Some biological aspects of
two species of fish (Heckel) BarbusLuteus and Barbus
grybus (Heckel) in AL-Habbania Lake. MSc thesis.College
of Education (Ibn Al–Haytham, Baghdad University. 95p.
Al-Shammaa, A. A. (1993). Preliminary study of Buni Barbus
sh a rpeyi in Al-Hammar mar sh - AlFoh ood – Iraq .
Mesopotamian Journal of Marine Science, 8(2) : 350-
Al-Zaidy, K. J. (2013). First recorded of Tilapia Zilli in AL-
Delmj Marsh weast AL-Diwania City Middle of Iraq. diyala
Agricultural Sciences Journal, 5 (1): 9 – 16.
Benavi de s, A. G., J. M. Canc in o and F. P. Ojeda (1994).
Ontogenetic chan ge in gut dimension s and microalgal
digestibility in the marine herbivorous fish, Aplodactylus
punctatus. Functional Ecology, 8: 46-51.
Canonico, G. C., A. Arthington, J. K. McCrary and M. L. Thieme
(2 005) . The effects of in trodu ced tila pi as on nat ive
bi od iver sity. A quatic Co n s erv a t ion: Marin e and
Freshwater Ecosystems,15(5): 463-483.
Dipper, E., C. Bredges and A. Menz (1977). Age, Growth and
feeding in the ballon wrasse lebursbergylta. J. Fish Biol.,
11 : 105- 120.
Duncan, D. B. (1955). Multiple rang and Multiple F test.
Biometric, 11-19.
Edmondson, W. T. (1966). Fresh water biology. 2nd ed. John
wily &sons ,New York, 1248pp.
Eli, A. (2005). 1524 Species in family Cichlidae (Cichlids). In:
Fish base Worl dWid e Web Elec tron ic Public ation. R.
Froese, D. Pauly (eds)
Food and Agriculture Organization of the United Nations (2012).
Cu l t u red Aqua t i c Sp eci e s In fo rmatio n P r ogr am
Oreochromis niloticus (Linnaeus,1758 ), Fisheries and
aquaculture Department:14pp.
Ghazwan, M. A. (2016). Alert to the most important species of
fish that ente red th e Iraq i aqu ati c environ men t and
recorded after 2003. Scientific Symposium, Research Center
and Museum of Natural History. Fish department.
Gordan, J. D. (1977). The Fish population inshore water of the
west costal Scotland. The food and feeding of the whiting
(Merlanguis merlanuis L.). Journal Fish. Biol., 11 (6):
Hyslop, E. J. (1980). Stomach content analyses- A review of
methods and their application. Journal Fish. Biol., 17:
Khalifa, S. Z. (2017). Environment and lifestyle of two fishes
Nile tilapia Oreochromis niloticus and the Blue tilapia
Oreochromis aureus in Tigris river south Iraq. MSc Thesis.
Agriculture college - Diyala university. 141p.
Mohamed, A. R. M. and M. O. Al-Jubouri (2017). fish assemblage
structur e in AL-Diwaniya river, middle of Iraq. Asian
Journal of Natural & Applied Sciences, 6(4):10-20.
Mutlaq, F. M. and A. J. Al-Faisal (2009). A new recording of two
in t r uder s spec ies of ti l api a f ish Ti l ap ia z illi an d
Oreochromis aureus in the south part in the main outfall
drain in Al-Basrah city. Journal of Marine Sciences, 2
Otieno, O. N., N. Kitaka and J. M. Njiru (2014). Length-weight
relationship, condition factor, length at first maturity and
sex ratio of Nile tilapia Oreochromis niloticus in Lake
Naivasha, Keny. International Journal of Fisheries and
Aquatic Studies, 2(2) : 67-72.
Popma, T. and M. Masser (1999). Tilapia life histo ry and
biology. SRAC. Publication N., 283.
Salih, K. I. (2007). The First record of Tilapia zilli in the natural
water (Eughrates River). The first scientific conference of
the agriculture college, Al-Basrah university. 26-27p.
ScientificSymposium (2012). Tilapia fish and its danger on the
Iraqi environment. Fish department. Museum of the natural
history. Baghdad university.
Shola, G. S., A. V. Offuene, T. M. Abubakar and O. V. Tosin
(2017). Gonad Somatic Index and Feeding Habit of Selected
Fish Species of Lake Kalgwaiin Jigawa State, Nigeria. Fish
& Ocean Opj., 4(2): 1-6.
Sinh a, V. R. P. and J. W. Jones (1967). On the food of the
freshwater eels and their feeding relationship with the
salmonids. Journal of Zoology, 153(1) : 119-137.
Stergiou, K. I. (1988). Feeding habits of the Lessepsian migrant
Siganus luridus in the eastern Mediterran ean, its n ew
environment. Journal of fish biology, 33(4): 531-543.
Trewavas, E. (1983). Tilapiine fishes of the genera Sarotherodon,
Ore ochromis and Danakilia. British Muse um(Natural
History), London, UK.
Turker, H., A. G. Eversole and D. E. Brune (2003). Effect of Nile
tilapia, Oreochromis niloticus (L.), size on phytoplankton
filtration rate. Aquaculture Research, 34(12):1087-1091.
Whitton, B. A. (1975). River ecology. Black well Sci. Pub.,
Oxford, 310pp.
464 Kareem Z. Negaud et al.
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
The fish species structure, occurrence, abundance and ecological indices of fish assemblage in the Al-Diwaniya River, middle of Iraq were studied. Fish were sampled monthly by different fishing gears from November 2016 to October 2017. Water temperature varied from 10.2oC in March to 32.8oC in August, dissolved oxygen values fluctuated from 5.0mg/l in August to 9.6mg/l cm in February, salinity ranged from 0.55‰ in April to 0.79 ‰ in July and pH values varied from 6.6 in August to 8.7 in March. A total 27 fish species belonging to eight families were collected, 19 of them were native and eight exotic species. The most abundant species were Carassius auratus, comprising 14.6% of the total catch, Planiliza abu (14.2%) and Oreochromis aureus (11.4%). The dominance ‎‏value (D3) was 40.2%. Water temperature showed significantly positive correlation with the number of fish individuals and weak positive correlation with the number of species, while salinity showed weak positive correlations with the number of species and the individuals. The mean annual values of diversity, richness and evenness indices were 2.56, 3.37 and 0.81, respectively. The study shows that the fish assemblage structure in the Al-Diwaniya River was clearly differed from adjacent rivers in middle of Iraq by number of fish species, the dominancy species and the fish diversity.
Full-text available
This study investigates gonado somatic index, food and feeding habit of selected fish species of Lake Kalgwai Jigawa State, Nigeria. Samples of fish were collected every fortnight (July 2012-June 2013) at three major landing sites of the lake. The weight of each fish was recorded, gonads were removed, weighed and the gonadosomatic index (GSI) calculated. Stomach was also removed and the content analyzed using frequency of occurrence and point method. Result obtained reveals GSI to range from 2.39±0.08% in Nile perch Latesniloticus [1] to 5.92±0.29% in Nile tilapia Oreochromisniloticus [1]. The stomach content analysis in this study distinguished the fish species into two major groups; Latesniloticus, Mormyrusmacrophthalmus Günther, 1866 and Bayad bagrus bayad Forsskål [2] were observed to exhibit carnivorous feeding habits and feed predominantly on crustacean, fish, fish parts, mollusks, insects and insect larvae, Oreochromisniloticus, African bony tongue Heterotisniloticus [3], Electric catfish Malapteruruselectricus, Synodotisnigrita and North African catfish Clarias gariepinus on the other hand were observed to have an omnivorous feeding pattern with plant parts, insect parts, detritus, crustaceans, snails, worms, fish parts, insects larvae, sand/mud, and algae dominating their diet. Many of the omnivores encountered in this study have good potential as future aquaculture candidate hence the need to further study their biology and their performance under captivity.
Full-text available
Fish samples (541) were collected every two weeks from different parts of Lake Naivasha using gill nets (50 mm to 150 mm mesh size) and beach seines (< 10 mm) between November 2013 and February 2014.The main focus of the study was on sex ratio, length-weight relationship and body condition of Nile tilapia. Results revealed that there were more males sampled with a sex ratio of male to female of 2:1. A comparison of the length-weight relationship for males and females showed that most of the fish had negative allometric growth (b<3) with males from Oserian and Hippo sampling stations point showing isometric growth (b=3). Length at first fish maturity of male and female fish obtained during this study was 17.7 cm TL and 18.0 cm TL respectively. The results from this study showed that fish in the lake are in good condition with condition factor value above 1.
Full-text available
Four different-sized (390±3, 140±2, 40±2, 16±1 g) Nile tilapia, Oreochromis niloticus (L.), stocked at the same biomass in timed pulse feeding chambers were provided 27–29°C water dominated by Microcystis (82%) and Scenedesmus (18%) to determine the effect of fish size on filtration rates. The number of Microcystis and Scenedesmus units filtered from the water decreased significantly with increasing tilapia size. The shaping constants and maximum filtration rates for Ivlev's feeding model used to describe the relation between filtration rates and the suspended particulate organic carbon (POC) concentrations were significantly different among the four sizes. Filtration rates of 763, 671, 512 and 300 mg C kg−1 h−1, which correspond to 70%, 82%, 86% and 90% saturation levels, were achieved at POC levels of 30, 32, 32 and 33 mg C L−1 for 16, 40, 140 and 390 g Nile tilapia respectively. Smaller tilapia achieved these rates at lower POC concentrations than larger tilapia.
1. Even though herbivorous fish have longer digestive tracts than carnivorous fish, a fact which agrees with optimal digestion theory, the existence of a relation between relative length of the digestive tract and capacity to digest and assimilate algal material has not been experimentally demonstrated. 2. We tested whether an increase in gut dimensions during ontogeny was associated with an increase in capability of fish to digest macroalgae in Aplodactylus punctatus. 3. Total gut length of this temperate marine fish increased from 43 to 237 cm as body length increased from 22 to 42 cm total length (TL). 4. Macroalgae, mainly fronds of the brown kelp Lessonia trabeculata, were the principal item found in their guts. 5. Individuals smaller than 30 cm had a higher proportion of invertebrate biomass in their gut than larger fish (40.6% and 0.3% of total content, respectively). 6. Transit time for Lessonia fronds increased as a function of body size, ranging between 20 h in fish 26.6 cm TL and 52 h in 40.0 cm fish. 7. Apparent digestibility of organic matter and total nitrogen increased as a function of body size from 38% to 80% when feeding on a Lessonia diet, and from 57% to 96% on a Ulva sp. diet. 8. These results explain why small herbivorous fish need to consume animal prey to satisfy their high mass-specific protein demands. 9. This study constitutes the first experimental demonstration in fish that an increase in relative gut length is associated with an increase in the capability to digest macroalgae. This allows larger fish to meet their energetic demands by consuming algae owing to their capability to digest low-quality food.
Methods for analysing fish stomach contents are listed and critically assessed with a view to their suitability for determining dietary importance—this term is defined. Difficulties in the application of these methods are discussed and, where appropriate, alternative approaches proposed. Modifications which have practical value are also considered. The necessity of linking measurements of dietary importance to stomach capacity is emphasized and the effects of differential digestion upon interpretation of stomach contents outlined. The best measure of dietary importance is proposed as one where both the amount and bulk of a food category are recorded.
Following the results of the cursory investigations made by Jones & Evans (1960,1962) into the predatory habits of eels we decided to enlarge on this work. Consequently we looked at the stomach contents of about 5000 eels. In addition and at the same time two Welsh streams carrying salmonids were selected and sampled specifically to try to determine the relationship in the feeding habits of eels and salmonids. The food of eels consisted mainly of trichopteran and dipteran larvae and plecopteran and ephemeropteran nymphs, though at times Gastropoda, Annelida, Crustacea and fish were common in the stomachs. Fish was not an important dietary item but, when eaten, the fish most commonly taken were elvers and eels. In the River Dwyfach the salmonids ate more or less the same type of food as the eels, but the trout ate more surface food than the young salmon. The similarity in feeding between the eels and salmonids resulted in apparent competition during the warmer months. In winter when the eels ate little the competition was thus almost negligible. Even though we speak of competition for the food available in the summer months we feel that before this can be accepted as fact we must know the relative abundance of each food organism eaten at this time.
The feeding habits of the Lessepsian migrant Siganus luridus in the eastern Mediterranean (Kastellorhizo Isle, Dodecanese, Greece) are examined. The stomach contents of 209 specimens, 131–250 mm total length, collected by bottom trammel nets, April 1985 July 1986, were analysed. Feeding intensity was high, although it significantly declined during the spawning period in summer. Siganus luridus feeds on a diverse assemblage of benthonic algae including 24 genera (seven green, eight brown and nine red algae) contributing 84.4% by weight (green algae 3%, brown 70.3%, red 11 %). Posidonia oceanica, diatoms, hydrozoa and sand were also found in the stomachs examined. On an annual basis, Dictyota sp., Cysloseira sp., Sphacelaria sp., Gelidium sp., Dictyopteris membranacea, Kuckuckia spinosa and Padina pavonica predominated in the diet. Diet overlap, on a weight basis, indicated a similar food spectrum during spring and summer which was different from that in autumn. The high feeding intensity of S. luridus during the year (except for the spawning period), its nonselective euryphagous nature, its high competitive potential, and its position in the food web of the eastern Mediterranean ecosystem are important characteristics that, along with suitable oceanographic and ecological conditions for the development and survival of young stages, have enabled the successful establishment and build-up of the population of this Lessepsian migrant in its new environment. Possible competitive implications in the eastern Mediterranean ecosystem are also discussed.