Eda, H.

Futagawa, M.

Matsumoto, S.

Morioka, S.

Zidana, H.K.

Aquatic Commons

Introduction
Ntchila Labeo niesops (Gunther) is an impor-
tant commercial cyprinid inhabiting in Lake
Malawi and its tributaries. This species is
known to breed in rainy season (Tweddle 1982)
and grows to over 40 cm in total length. Stock
decline of ntchila in Malawi has been observed
since early 1960s (Walker 1976), leading to ne-
cessity of stock assessment and artificial seed
production for both stock enhancement and
aquaculture promotion of the species.
Mass production techniques of artificial seed
of L mesops were first established in late 1990s
by the project of Japan International Coopera-
tion Agency "Aquaculture Development of In-
digenous Species in Malawi" at National Aqua-
culture Centre, Fisheries Department, Ministry
of Natural Resources and Environment, Ma-
lawi, following the preliminary attempt of
Msiska (1986). However, morphological abnor-
mality was frequently observed in hatchery-
reared specimens of this species. It is wefl
known that higher abnormality rate occur in
hatchery-reared fish than the wild ones, such as
in Pagrus major (Matsuoka 1987), Opleg-
nathus Jàsciatus (Shirnizu & Fujita 1985),
Plecoglossus altivelis (Takashima et al. 1976)
etc. For aquaculture promotion as well as stock
enhancement of fish species, quality control,
13
e.g. reduction of abnormality occurrence in
hatchery-reared specimens, is a crucial issue to
be considered. This study aimed at identifying
and describing the abnormality occurring in
vertebrae of hatchery-reared Labeo mesops ju-
veniles.
Materials and Methods
A total of 30 Labeo mesops laboratory-
hatched juveniles (56 day-old) were available in
this study. Total length (TL) of fish ranged
from 16.00 — 26.50 mm (mean ± SD: 21.50 ±
2.76 mm TL). They were obtained from Na-
tional Aquaculture Center, Fisheries Depart-
ment, Domasi, Malawi. Broodstocks were cap-
tured from Shire River in Liwonde National
Park, Malawi. Eggs were obtained by natural
spawning after maturation by pituitary hormone
injection. Hatching took place Qfl 14 March
2002 and fish were reared in 200 1 plastic tank.
Zooplankton (rotifers, copepods etc.) collected
from the earthen pond was given twice a day at
the density of 5 — 10 md. per ml water.
Fish samples were preserved in 5% formalin
immediately after collection. After 110 days
preervation in 5% formalin, fish were treated
to be double stained transparent specimen, fol-
lowing the method described by Kawamura and
Hosoya (1991)(Fig. 1). Using these specimens,
Aqtia-FLrh Technical Report Issue No: I Nov 2002
Abnormality ôfvertebrae in hatcheryreared ntchila Labeo mesops
(Gil nther, I 868) (Pisces : Cyprinidae) juveniles
S. Morioka', if Eda2, M. Futagawa2, S. Matsumoto' & II. K. Zidana2
'Dept of Aquaculture & Fisheies Science, Bunda College of Agriculture, University of Malawi, cc. 219
Lilongwe, Malawi. E-mail : morioka@malawLnet
2National Aquaculture Centre, Fisheries Department, Ministry ofNatural Resources & Environment
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Aqua-Fish Technical Report
abnormalities occurring in vertebrae were iden-
tified and described.
Results and Discussion
Number of vertebrae in Labeo mesops was 37
and the rate of abnormality occurrence in verte-
brae was 60 % (18 of 30 fish). The following
abnormal symptoms were identified;
C
0
C
25
20
15
centra urostyle
fusion
•ii-!;ii] [I]
deformation
B
C L1L1±*pL1J
undeveloped centra
Fig. 2. Abnormality types observed in this study.
Issue No: 1 Nov 2002
A
Fig. I. Vertebrae of hatchery-reared ntchila Labeo
mesops juvenile (21.05 mm TL). Bar indicates
1.00 mm.
abnormal bend
18
16
14
12
10
8
6
4
2
rrk T1 -l
1 6 11 16 21 26 31 36
Ve'tebra number
Fig. 3. Position of abnormality in vertebrae of Labeo mesops juveniles.
30
± ±
Fig. 4. Total length (mm) of fish with normal and
I abnormal vertebrae. Vertical bars indicate standard
deviations.
14
Normal Abnormal
Aqna-Fish Technical Report Issue No: 1 Nov 2002
- fusion of neighboring vertebrae (n- 14) (Fig.
2A).
deformation of vertebrae (n = 7) (Fig. 2A),
- abnormal bend of vertebrae (n 5) (Fig. 2B),
undeveloped (small) vertebrae (n 4) (Fig.
2C).
Fusion and deformity symptoms appeared as
combined, i.e. deformed vertebrae fusing with
its neighboring vertebrae (Fig. 2A). Abnormal-
ity in vertebrae mainly appeared in caudal por-
tion around 34th — 37111 vertebrae and urostyle
(17 of 18 abnormal fish) and occasionally in
abdominal portion (2 of 18)(Fig. 3). Similar
symptoms and position of abnormality occur-
rence were reported in Thunnus oriental/s
(Shimizu & Takeuchi 2002), Total length of
abnormal fish ranging between 16.00 and 26.05
mm (mean ± SD: 21.48 ± 2,86 mm) were not
significantly different from fish with normal
vertebrae ranging beteen 18.00 and 26.50 mm
TL (mean ± SD: 21.53 ± 2.73 mm) (F> 0,05, t-
test, Figure 4). This seems to indicate that there
is no sizebias in abnormality occurrence. How-
ever, considering the possibility of mortality in
smaller / abnormal specimens before collection,
seial observations since hatch i ng are required
to álarifying size bias of abnormality occur-
reice nd relationship between abnormality and
mortality.
One of factors causing abnormality in hatch-
ery-reared fish is considered to be unbalanced
nutrition in diet, e.g. deficiency in essential
amino acid (EAA), essential fatty acid (EFA)
and minerals etc. In particular, deficiency of
EFA iii nauplii of Anemia Spp. is known to
cause high rate of abnormality occurrence in
several fish species (Kanazawa 1988). In this
study, fish were given natural zooplankton that
are cusidered to have betternutritional values
than Aeniiaspp. (Kanazawa 1988) in supply-
ing EFA, Ho'vever, nutritional requirements of
Labeo mesops has never been investigated so
far and this needs to be clarified. In Pagrus ma-
jor. the relationship between undeveloped
uniflated swim-bladder and lordic deformity in
vertebrae was reported (Kitajima el al. 1981).
Peak spawning season of L. mesops is esti-
mated to be during early rainy season, that is,
from November to January. Broodstock used in
15
this study was collected in March 2002, being
in the last phase of rainy season. The egg size
was also inconsistent. This may reveal that eggs
used in this study were of lower quality than
what would be obtained during peak spawning
season. However, studies on egg quality in L.
mesops have so far not been made. Thus, com-
parison of seasonal differences in egg quality of
this species is needed.
Acknowledgements
Authors express great thanks to Mr. P.B.
Kataya, National Aquaculture Centre, Domasi,
Malawi, for assistance of fish rearing. We are
also grateftil to Japan International Cooperation
Agency (JICA) for giving us an opportunity to
work on this subject.
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16



Abnormality of vertebrae in hatchery-reared ntchila Labeo mesops (Gunther, 1868) (Pisces: Cyprinidae) juveniles

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Abnormality of vertebrae in hatchery-reared ntchila Labeo mesops (Gunther, 1868) (Pisces: Cyprinidae) juveniles

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