International Journal of Animal and Veterinary Advances 1(2): 66-72, 2009
ISSN: 2041-2908
© M axwell Scientific Organization, 2009
Submitted Date: August 17, 2009
Accepted Date: September 24, 2009
Published Date: October 30, 2009
A Study of the Length -Weight Relationship and Condition Factor of Callinectes
amicola (De Rochebrune, 1883) from Okpoka Creek, Niger Delta, Nigeria
1
1
J.F.N. Abowei and 2 A.D.I. George
Department of Biological Sciences, Faculty of Science, Niger Delta University, Wilberforce
Island, Amassoma, Bayelsa State, Nigeria.
2
Departm ent of Fisheries and A quatic Environment, Faculty of Agriculture, Riv ers State
University of Science and Technology, Port Harcourt, Rivers State, Nigeria.
Abstract: The length - weight relationship and condition factor of Callinectes amicola from O kpoka C reek in
the Niger Delta area of Nigeria was studied for a period of one year. The exponent ‘b’ values for all the sexes
ranged from 2.336 and 2.56 (males), 2.367 and 2.536 (females) and 2.352 and 2.548 (combined sexes)
respectively. Growth generally exhibited a negative allometry in all the sexes as shown by the mean exp onents
(b=2.448) for male, female (b=2.451), combined sex (b=2.449). Generally, the regression equations revealed
high correlation in all the sexes as the correlation coefficient (r) values for male (0.951), female (0.971) and
combined sexes (0.961) are very close to r = 1. The monthly K values of the males ranged from 0.0984 and
0.1503 (mean = 0.1214). The estimated K value for both sexes combined was 0.1260. Similarly, estimated K
values for the females ranged from 0.0889 – 0.1524.The overall mean K value for the females was 0.1229. The
minimum K value (0.098 4) for the male was observed in February. The female C. am nicola minimum K value
(0.0889) an d Kmax (0.158 0) valu es w ere ob tained in No vem ber.
Key w ords: Callinectes amicola, length -weight relationship, cond ition facto r, Okpoka Cre ek an d Nigeria
INTRODUCTION
The blue crab Callinectes amnicola belongs to the
family Poruntidae. It is famous and one of the most
important economic swimming crabs present in the
brackish wetland and lag oons in Nigeria (Abbey-Kalio,
1982; Solarin, 1988). These crabs inhabit muddy bottoms
in mangrove areas and River mouths (Defelice et al.,
2001). This crustacean in the most important food
organism caught in the coastal (inshore) fishery and
lagoons in west Africa (Lawal-Are et al., 2000). The
species is generally cherished source of protein and
minerals in human diet and animal feeds (Chindah et al.,
2000; Em man uel (20 08).
These crabs are gonochoristic and physiological
maturity in males in reached when the carapace attains a
length of between 90 and 110 mm . The male and female
usua lly begins their mating process wh en a female is in a
premolting condition. The crabs remain paired for 3 to 4
days until the female molts and the n they copu late
(Knuckey, 1996). The fem ale then migrates offshore with
the fertilized eggs, where they hatch in a couple of weeks.
They can deliver an extremely painful pinch and are
noted for being particularly aggressive and difficult to
handle safely. Even when out of the water, they will lunge
towards m ovemen t they consider a threat.
Blue crabs are blue because their she ll contains a
number of pigments, including Alpha-crustacyanin, which
interacts with a red pigment, astaxanthin, to form a
greenish-blue coloration. When the crab is cooked, the
Alpha-cru stacyanin breaks down, leaving only the
astaxanthin, which turns the crab red-orange.
Length-weight relationship (LW R) and its parameters
‘a’ and ‘b’ are of great impo rtance in fishery biology and
practical assessment of stocks of aquatic species (Gulland,
1983; Enin, 199 4; Stergiou and M outopou los, 2001).
Pauly (1993) suggested the following situations when
length-weight relationship may be needed .
C
C
C
C
The conv ersion of length of individual fish to we ight.
Estimating the mean weight of fish of a given length.
Conversion of growth equation for length into a
growth equation for weight, and
Morphological comparisons between populations of
the sam e species or b etween species.
L W R can also be useful in studies of gonad de velop men t,
rate of feeding, metamorphosis, maturity and well being
of the fish p opulation (L e Cre n, 1951; Bolger and
Connolly, 1989). Length-weight relationship data may be
incorporated into a database such as fish base (Froese,
1990; Pauly and Froese, 1991) for easy access, retrieval
and use for any assessmen t work.
The growth exponent ‘b’ in the LWR has values
between 2 and 5 (Bagenal and Tesch, 1978). They
observed that when the expon ent ‘b’ is 3, it indicates
Corresponding Author: J.F.N. Abowei, Department of Biological Sciences, Faculty of Science, Niger Delta University,
Wilberforce Island, Amassoma, Bayelsa State, Nigeria.
66
Int. J. Anim. Veter. Adv., 1(2): 66-72, 2009
area of 206Km 2 and extends 7Km offshore to a depth of
about 7.5 metres (Irving, 19 62, Scott, 1966 and Alalibo,
1988). The Bonny River is a major shipping route for
crude oil and other cargoes, and leads to the Port Harco urt
quays, Federal Ocean Terminal, Onne, and Port Harcourt
Refinery company terminal jetty, Okirika. Specifically,
the Okpoka creek lies between Longitudes 7 ° 03! and
7 ° 05! East and Latitudes 4° 06! and 4°24! and it is about
6 kilom eters lon g.
Characteristically, the area is a typical estuarine tidal
water zone with little fresh water input but with extensive
mangrove swamps, inter-tidal mud flats, and influenced
by semi-diurnal tidal regime. In the Bonny River estuary,
the salinity fluctuates with the sea son and tide regime is
influenced by the Atlan tic ocean (D angana, 1985). Tidal
range in the area is about 0.8m at neap tides and 2.20m
during spring tides (N ED EC O, 1961).
It is strategically located southwestern flanks of Port
Harco urt and O kirika of Rive rs State. The creek is
bounded by thick mangrove forest dominated by
Rhizophora species interspersed by White mangrove
(Avecinia sp.) and Nypa palm. Along the shores of the
creek are located the Port Harcourt Trans- Amadi
Industrial layout, several establishments, markets, the
main Port Harcourt Zoological garden and several
commu nities. The communities are Oginigba, Woji New
layout, Azuabie, Okujagu- Ama, Ojimba- Ama, Abuloma,
Okuru- Ama, Oba-Ama and Kalio- Ama.
Artisanal fishers mainly exploit the fisheries. The
fishers use wooden/dug-out canoes ranging in size from
3 to 8m long. T he canoes are either pad dled or powered
by small outboard engines, and manned by an average of
two men. From these boats, the fishers operate their cast
nets, hook and lines, gillnets, crab pots, etc.
isometric growth (without changing body shape) but when
below or abo ve 3, growth is allometric (i.e., fish changes
shape as it grows larger).
How ever, Pauly (1993) while lam enting on the lack
of adeq uate theory to guide research w ork an d form ulate
testable hypothesis on the LWR of fish and aq uatic
invertebrates, stated that “there is no theory tha t tells us in
which case estimated b value can be expe cted to be below
3 (negative allom etry) or above 3 (positive allometry).
The condition factor is an estimation of the general
well being of fish and crustaceans (Oni et al., 1985; Jones
et al., 1999). It is based on the hypothe sis that heavier
individuals of a given length are in better condition than
less weightier ones (Bagenal and Tesch, 1978). Condition
factor has been used as an index of growth and feeding
intensity. W eatherly and Rogers (1978) posited that
condition factor of different populations of same species
is indicative of food supply and timing and duration of
breed ing.
Consequently, several studies have been carried out
in this regard for finfish species and crustaceans. Notable
among these are the reports of Stickney, (1972) on fishes
and invertebrates in Georgia Coastal water, Georgia. Olm i
and Bishop , (1983) on the blue crab Callinectes sapidus
Rathbun from the Ashley River, South Carolina; Prasad,
et al., (1989 ) on three Portunid crab species;
Enin, (1994) on two W est African prawns
(Nematopalaemon hastatus and Macrobrach ium
macrobrachion) from the C ross River estuary, Nigeria;
Enin, et al., (1996) on estuarine prawn Nematopalaemon
hastatus off the South East coast of Nigeria; Sukumaran
and Neelakantan (1997) on two marine Portunid crabs
(Portunus sanguinolentus and Portunus pelagicus) from
the Kamalaka coast, India. Villasm il et al., (1997) on the
blue crab Callinectes sapidus in Lake M aracalbo, C lencia
(Ma racalbo); Tabash (2001) on the blue crab Callinectes
arcuatus in the Gulf of Nicoya, Costa Rica; Atar and
Secer (2003) on the blue crab (Callinectes sapidus in
Beymelek Lagoon lake, Antalya, Turkey and Yakub and
Ansa (2007) on the pink Shrimp Penaeus notialis and
Giant tiger shrim p, Penaeus monodon of Buguma creek
in the N iger D elta, Nigeria.
There is a dearth of information on length-weight
relationships on the swimming crabs (Genus Callinectes)
from Nigerian waters pa rticularly fro m the Niger Delta
estuarine waters for the evaluation of its ecology with a
view to effectively m anag e the resourc es for su stainable
supply to the citizenry.
Sampling stations: Six samp ling stations were
established along a spatial grid of the Okpoka creek
covering a distan ce of about six kilometers. The sampling
stations were established based on ecological settings,
vegetation and h uma n activities in the area. The sampling
station is about one kilometer apart from each other.
Station 1: Located upstream of the Po rt Harc ourt m ain
abattoir at Oginigba waterfront with living houses on the
left flank of the shoreline. Vegeta tion is sparse w ith
mainly red mangrove (Rhizophora sp.,) white mangrove,
Avicenia sp. and Nypa palm (Nypa fructicans).
Station 2: Situated at Az uabie / Port H arcourt m ain
abattoir waterfront. It is located downstream of Station 1.
The bank fringing the Azuabie/abattoir is bare with no
visible plants except toilet houses, residential houses,
animal pens, boats and badges, while at the opposite side
there are few mangrove and Nypa palm. Human activities
here include slaughtering of animals, marketing, fishing
and boat building. It is located downstream of station 1
and it is main collection point of abattoir wastes and other
human and market wastes.
MATERIALS AND METHODS
Study Area: The study was carried out in Okpoka creek,
which is one of the several adjoining creeks off the Upper
Bonny Rive r estuary in the Niger Delta (Fig. 1). The
Bonny River Estuary lies on the Southeastern edge of the
Niger Delta, between longitudes 6°58! and 7°14!! East,
and latitudes 4°19!! and 4°34! North. It has an estimated
67
Int. J. Anim. Veter. Adv., 1(2): 66-72, 2009
Fig. 1: Map of Niger Delta showing Rivers State and the Study Area.
Station 3: It is dow nstream from the Port Ha rcourt
abattoir at the Woji sand-Crete. It is about one kilometer
away from Station 2. The major activities here included
sand mining and loading.
Station 5: Is situated at Ojimba cum Abuloma
waterfronts. There are no commercial activities apart from
ferryboats operations. The shoreline fringes have mainly
Nypa palm. The area is shallow and at low tide, the
greater part of the bottom mud flat is exposed.
Station 4: This station is located at Okujagu-Ama area.
There are no industrial activities here. Mainly fishers
occupy the area. Nypa palm dominates the marginal
vegetation while the op posite side is thickly populated
with red mangrove forest. Rhizophora racem osa and
Rhizophora mangle. The main activity is fishing, boat
ferrying and occasional sand moving.
Station 6: Is located in front of Kalio-ama directly
between Okpoka and Amadi creeks. The human activities
here include jetty operations, oil and non-oil industrial
activities, boat traffic and fishing. Vegetation is few
dominated by red man grove interspersed with wh ite
mangrove Avicenia africana.
68
Int. J. Anim. Veter. Adv., 1(2): 66-72, 2009
Table 1: Least squ are reg ressio n eq uatio n, ex pon ent (b ), interce pt (a), c orrela tion c oeff icien t (r) and rang es o f
Ca llinecte s am nico la
Sex
Regression
r
b
Equation
M ale
W = - 2.356L 2 . 4 4 8
(0.935-0.963) 0.951
(2.336-2.561) 2.448
Fem ale
W = - 2.392L 2 . 4 5 1
(0.962-0.978) 0.971
(2.367-2.536) 2.451
Comb ined sex
W = - 2.373L 2 . 4 4 9
(0.948-0.970) 0.961
(2.352-2.548) 2.449
() = Range values
the Length-W eigh t relatio nsh ip in
a
(-2.156 to -2.688) -2.356
(-2.215 to – 2.496) -2.392
(-2.215 to -2.592) -2.373
millimeter (mm) while weight measurement was done
using a 0.001g precision Adam (PGW series) weighing
balance to the nearest gram s (g).
The length-weight relationships of all samples
collected were determined for the various sexes by the
expression:
W = aL b (Le Cren, 1951; Pauly, 1983)
(1)
W here:
W = the derived weight (a)
L = th e carapace length (mm ) or width
a = the intercept of the regression curve
b = the regression coefficient (slope)
The parameters ‘a’ (intercept) and ‘b’ (slope) are easily
estimated by the linear regression based on Logarithms as
Plate 1: Crab traps and other fishing materials
LogW = Log a + blogL (Lagler, 1968)
Sample collection: The crabs for study were collected
fortnigh tly for twe lve (12 ) calendar m onths (January to
Decembe r, 2007) using the square lift ne t trap (Plate 1) at
each of the sa mpling stations along the Okpoka creek.
The lift net trap has a sq uare structure made of wooden
stick of about 4cm thick and an area of 4.9m 2 . The mesh
sizes of the bag-like net were 1.2cm to 2.0cm
multifilament nylon. The length of the bag is 40 to 60 cm.
Strong nylon cords were woven in a net-like fashion from
the centre to the middle of each of the four edges. A twine
of about 6m long w as attached to the centre and the other
free end of the twine was tied to a floater, which served as
a marker on the water surface to show the position of the
gear.
The lift net trap was baited at the centre with animal
offal and fish. The trap was operated from a hand-paddled
canoe manned by two persons; one rowing while the other
sets and hulls the trap into and from the water. The crabs
were caught trapped and most of them were observed
feasting on the bait until they were hulled into the boat.
Sampling lasted for 4 hours on every sampling day and
samples were collected between low ebbing and low
flooding tide periods. The catches were taken to the
laboratory in a cooler and stored in a deep freezer for
further analysis.
Crabs were identified to species level carried out
using photo cards and availab le identification keys
(Fischer, 1978; Williams, 1974; Schneider, 1990).
Therefore each crab was sorted into species, sex and the
required metric measurements were taken.
The carapace w idth and length w ere measured w ith
a 0.5mm precision vernier caliper to the nearest
(2)
The pattern of grow th (isom etric or allometric) in
C.amnicola was determined from the value of ‘b’ in the
equation W = aL b . The linear regression routine option 3
in FiSAT (FAO – ICLA RM Stock Assessm ent Tool)
software (Gayanilo et al., 1995) using Plll 950 MHZ
computer for the analysis. In the analysis, only the midLengths and mean weights of the classes are required by
FiSA T (Gayanilo and Pauly, 199 7).
The Fulton’s condition factor (K) was estimated from
mean length and mean weight in the sample using the
relationship
K = 100 W (Gayanilo et al.,1997)
L3
W here:
K = Condition factor
W = mean weight of crab (g)
L = mean length of crab (mm)
(3)
RESULTS
The results of length-weight relationship (L W R)
study using the log-log transformation an d linear square
regression analysis meth od are presented in Table 1.
The exponent ‘b’ values for all the sexes ranged from
2.336 and 2.56 (males), 2.367 and 2.536 (females) and
2.352 and 2.548 (combined sexes) respectively (Table 1).
The grow th gen erally exhibited a negative allometry in all
the sexes as shown by the mean exponents (b = 2.448) for
male, female (b = 2.451), combined sex (b = 2.449). The
scatter diagrams for the length weight relationship for
69
Int. J. Anim. Veter. Adv., 1(2): 66-72, 2009
Table 2: M onth ly Condition factor for male C alline ctes a mn icola in
Okpoka C reek
M onth
Co ndition f actor
Jan.
0.1115
Feb.
0.984
March
0.1247
Ap ril
0.1294
May
0.1453
June
0.1503
July
0.1236
Aug.
0.108
Sep t.
0.1214
Oc t.
0.1238
Nov.
0.1055
Dec.
0.1144
Tab le 3: Mon thly Condition factor for female Ca llinecte s am nico la in
Okpoka Creek.
M onth
Condition factor
Jan.
0.0966
Feb.
0.1099
March
0.1289
Ap ril
0.1524
May
0.1041
June
0.1416
July
0.1256
Aug.
0.0989
Sep t.
0.1351
Oc t.
0.1339
Nov.
0.0889
Dec.
0.1006
Fig. 3: Length-Weight relationship of female C. amnicola
Fig. 4: Length-Weight relationship of Combined sexes of
C. amnicola
the minimum K value (0.0889) and Kmax (0.1580) values
were obtained in Novem ber.
DISCUSSION
The observed values of the regression coefficient (b)
for the males, females and combined sexes (male = 2.448,
Fem ale = 2.451 and com bined sexes = 2.499) less than 3
are indication of negative allom etric growth. This is in
agreement with the results from Badagry, Lagos and
Lekki lagoons for the same species by (Law al-Are, 2003).
The b values obtained in this study also agreed with
values obtained for C. sapidus from G eorgia (Stickney,
1972) and Beymelek Lagoon Lake, Turkey (Atar and
Secer, 2003). How ever, these results are contrary to what
was observed in Lag os lagoon and it ad jacent creeks on
the same species by Emmanuel, (2008), who reported a
positive allometric grow th for C. amnicola. Akin-Oriola
et al (2005) also reported b>3 (positive allometric growth)
for Callinectes pallidus from Ojo Creek in Badagry,
Lagos state.
Generally, the regression lines revealed a high
correlation in all the sexes since the correlation coefficient
(r) values are very close to unity. This observation is
indicative of a very positive correlation between carapace
length and total weight in this species. This agree d with
Fig. 2: Length-Weight relationship of male C. amnicola
male, female and combined sexes are illustrated in Fig. 2,
3 and 4 respectively. Generally, the regression equations
revealed high correlation in all the sexes as the correlation
coefficient (r) values for male (0.951 ), female (0.971) and
combined sexes (0.961) are very close to r = 1.
The results of the monthly mean condition factor (K)
for the males an d fem ales, C. am nicola are shown in
Tables 2 and 3 respectively. The monthly K values of the
males ranged from 0.0984 and 0.150 3 (mean = 0.12 14).
The estimated K value for both sexes combined was
0.1260. Similarly, estimated K v alues for the females
ranged from 0.0889 – 0.1524.
The overall mean K value for the females was
0.1229. The minimum K value (0.0984) for the male was
observed in February In respect of the female C. am nicola
70
Int. J. Anim. Veter. Adv., 1(2): 66-72, 2009
the report on the same species from Badagry, Lagos and
Lekki Lagoons by (Lawal-Are, 2003) and the results on
the species from Lagos lagoon and adjacent creeks by
Emmanuel (2008). Similar trend was also observed on
two Macrobrachium macrobrachium by (Enin, 19 94) in
the Cross River estuary of Niger Delta.
The results of the condition factor were neither sex
nor season dependent. There was no significant variations
(#0.05) between sexes. The similarity of the condition
factors in the male and female crabs may be attributed
probably to the absence of ov igerou s females.
Branco and Masunari (2000) reported difference in
condition factor of male and female Callinectes danae
from Conceicao Lagoon sy stem, Santa Catarina, Brazil.
They observed that it was probably due to higher weight
of the female gonads of the crabs. However, in contrast to
this result, Lawa l-Are and Kuse miju (2000 ) and
Emmanuel (2008) observed differences in the co ndition
factor of the different sexes of Callinectes amnicola in
Badagry Lagoon and Lagos Lagoon and its adjacent
creek .
Law al-Are and K usem iju, (2000) reported higher
condition factor in male than females crab s in Bada gry
Lagoon Nigeria. Also while Emmanuel, (2008) observed
in his study at Lagos Lagoon and its adjacent creek higher
condition factor in the males than the female crabs. H e
also observed that condition factor was lower in the
smaller crabs.
In fact, Warner (1977) reported that in true crabs, the
males showed a higher condition factor than the females.
This supports the slightly higher mea n K value (0.1260)
of the male than that of the female (K = 0.1229) observed
in this study. The non-seasonality, non significant
variations between sexes may be related to food regime of
the crab species utilizing food resources and accumulating
a large quantity of flesh as was also observed by Ikomi
and Sikoki, (2001) for fish in their study.
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