Condition, Length-Weight Relationship, Sex Ratio and Gonadosomatic Index
of Indian Mackerel (Rastrelliger kanagurta) Captured from Kuantan Coastal
This study described the Condition factor, Length-Weight relationship,
Gonadosomatic index and sex ratio of Indian mackerel (Rastrelliger kanagurta)
which is an important fish in the Kuantan coastal water, Malaysia. Data were
obtained from December 2011-May 2012 and a total of 1064 Indian mackerel specimens
were studied in this research. The result showed that male Indian mackerel was
significantly more than female (χ2 = 7.91; p<0.01) in the
population in the Kuantan coastal area. Length-Weight relationship of each month
was significant (p<0.01) with all coefficients of determination (R2)
values being higher than 0.72. The allometric coefficients (b) of length-weight
relationship varied between 2.5128 (April) and 3.0807 (May). A negative allometric
growth of Indian mackerel was observed in January, March and April. An isometric
growth was observed in December and February while a positive allometric growth
was observed only in May. The b-value of the length-weight relationship of Indian
mackerel in April was very low compared to other month. The condition factor
ranged from 1.0499-1.1320 and was significant difference between months (p<0.05).
The significantly lowest mean condition factor was found in December and the
highest in February and April. Overall higher mean condition factor was observed
in smaller fish of both sex. The overall mean condition factor of female was
better than male. Gonadosomatic index of Indian mackerel in February was higher
than those observed in March and April and followed by May. Gonadosomatic index
rapidly increased after January and reached at peak in February and decline
after February. A positive relationship was observed between gonadosomatic index
and condition factor of Indian mackerel. The peak spawning season of Indian
mackerel in Kuantan coastal water was from February to April. The spawning season
of Indian mackerel in Kuantan coastal water falls within the period between
end of January and end of May.
Received: October 01, 2012;
Accepted: October 05, 2012;
Published: January 10, 2013
Fisheries industry plays an important role in the economy of many countries
including Malaysia. In Malaysia, fisheries sector contributed 1.2% to GDP (Gross
Domestic Product) in 2008 which was increased by 1.3% in 2009. However, the
world fisheries have been showing poor capture production since the last decade
(FAO, 2011). In 2000, the global capture production was
about 950 million MT and in 2010 the capture production was decreased nearly
900 million MT. However, the total capture production in Malaysia has increased
in the last decade. Since, year 2000 (1.2 million MT) the total capture production
in Malaysia has increased by 10% (FAO, 2011).
Marine fisheries sector is of fundamental importance to Malaysia in terms of
revenue generation, employment and food security. In 2009, the total production
of marine fisheries was nearly 2 million MT and it valued nearly 9000 million
Malaysian Ringgit which contributed 1.3% to the Malaysian GDP (Gross Domestic
Product). Besides this, this sector provided nearly 150 thousand jobs directly
and/or indirectly (DOF, 2009). In Malaysian about 60-70%
of total animal protein is supplied by marine fisheries (Lihan
et al., 2006) which is dominated by a wide variety of fish species
(e.g., Indian mackerel, slimy mackerel, yellow striped scad, bleeker smoothbelly
sardinella, smoothbelly sardinella, kawakawa, longtail tuna and torpedo scad,
Among variety of fishes, Indian mackerel is one of the important fish in Malaysia.
Indian mackerel is coastal pelagic species, often found in a large shoal at
a depth range of 20-90 m (Pauly et al., 1996).
Adults Indian mackerel feed on macro plankton such as larval shrimps and fish.
Spawning occurs in several batches with eggs fertilized externally. Both eggs
and larvae of Indian mackerel are pelagic (Collette, 2001).
It is widely consumed in many parts of Malaysia due to its abundance,
ease in the capture and low market price. In 2010, the capture production of
Indian Mackerel was 186225 MT and it accounts for 10% of total capture fish
production. However, in Malaysia, total capture production of many marine fishes
is decreasing day by day. Therefore, management of wild population is necessary
for an urgent basis to obtain sustainable capture production.
Understanding population dynamics in particular their stock condition, growth,
spawning seasons, recruitment, mortality, etc. are prerequisite before identifying
proper management techniques on any wild fish stock. There is some information
about wild population of Indian mackerel. Unfortunately, such information of
most fishes including Indian mackerel on the east coast of peninsular Malaysia
especially in the Kuantan area is lacking. As a starting point, this research
quantifies some population parameters namely condition factor and its temporal
variation, length-weight relationship, gonadosomatic index of Indian mackerel
populations in the Kuantan coastal water, Malaysia. The objectives of this study
were (1) to determine length-weight relationship of Rastrelliger kanagurta,
(2) to determine the condition factor of Indian mackerel and (3) to determine
gonodosomatic index and spawning season of Indian mackerel.
MATERIALS AND METHODS
Area of capture and sample collection: All fishes were collected early
in the morning from Kompleks Lembaga Kemajuan Ikan Malaysia (LKIM), Kuantan,
Pahang, Malaysia. All fishing vessels used purse seine nets to catch Indian
mackerel and Fig. 1 shows the area of capture of Indian mackerel
based on the information received from fisherman. Fishing vessels were equipped
with icing systems and fish were kept at lower temperature to keep fresh. In
this experiment, all fish samples were collected before sorting to avoid biasness
on size. After collection, they were immediately preserved with ice in the ice
box and transported to the laboratory. Samples were collected monthly for a
period of 6 months (December to May, 2012). A total of 1064 Indian mackerel
was sampled in this study.
|| Map showing area of Indian mackerel capture
Sample measurement: Upon arrival at the laboratory, total Length (L)
and Standard Length (SL) of fishes were measured using a special measuring board
with a meter rule calibrated in centimeters, Fish length was measured to the
nearest centimeter. Body weight (W) of 2 decimal points was measured after blot
drying with a piece of clean tissue. After recording length and weight of fish,
it was dissected to collect gonad and determine the sex. All gonads were weighted
with a digital balance. In some cases, the gonad was not developed. In those
cases the sex of fish was unidentified. The length-weight relationship was calculated
using the Equation (Pauly, 1983, 1993):
where, W is the weight of fish (g), coefficient a is the intercept in
the y-axis, regression coefficient b is an exponent and L is the total length
of fish (cm). The value of b indicates isometric growth when close to 3. The
statistical significance level of R2 was estimated and the parameters
a and b were estimated by linear regression analysis based on the natural logarithms:
Additionally the coefficient of determination r2 were estimated.
The Fultons Condition factor
(K) for each experimental fish has been calculated using the formula:
where, K is the Condition factor, W is the Weight of fish, L is the Total length
of fish (cm).
Gonadosomatic index (GSI) was calculated using the Equation:
Statistical analysis: All regressions and correlation were statistically
analyzed using SPSS (version 16.0) which was also applied to differing between
months on condition factors and gonadosomatic index. Difference between monthly
condition factors and gonadosomatic index were analyzed through the analysis
of variance (ANOVA) and the difference between sex ratio was analyzed through
the Chi-square (χ2) test.
Length-Weight relationship: Monthly of Length-Weight Relationships (LWR)
of Indian mackerel were presented in Table 1 and Fig.
2. LWRs of Indian mackerel in all months were found to be linear. LWRs showed
that the allometric coefficients vary between 2.5128 (April) and 3.0807 (May).
LWRs of each month was significant (p<0.01) with all coefficients of determination
(R2) values being higher than 0.72. A negative allometric growth
of Indian mackerel was observed in January (W = 0.0155L2.8839, r2
= 0.8484, p<0.01) (Fig. 2b), March (W = 0.0135L2.9298
,r2 = 0.8193, p<0.01) (Fig. 2d) and April
(W = 0.0483L2.5128, r2 = 0.7261, p<0.01) (Fig.
2e). An isometric growth was observed in December (W = 0.0098L3.0244,
R2 = 0.8841, p<0.01) (Fig. 2a) and February
(W = 0.0113L3.0015, R2 = 0.8141, p<0.01) (Fig.
2c) while a positive allometric growth was observed only in May (W = 0.0086L3.0807,
R2 = 0.8840, p<0.01) (Fig. 2f).
Condition factor: The condition factor (K) ranged from 1.0499-1.1320
(Fig. 3). Condition factor was significantly different between
months (p<0.05). The significantly lowest mean K value was found in December
and the highest was in February and April. The mean condition factor in February
was comparatively slightly higher than in April, although they were statistically
same (p>0.05). The mean condition factors in January, March and May were
significantly lower than in February and April and significantly higher than
in December. The mean condition factor (Km) in relation to size class
for both sexes is shown in Fig. 4. Overall higher Km
was observed in smaller fish of both male and female. Overall Km
of female was better than male.
Sex ratio: Out of the total of 1064 specimens of R. Kanagurta
collected from December 2011 to May 2012, only 329 were able to determine the
sex. Out of 329, 190 (57.75%) were males and 139 (42.25%) were females.
|| Monthly descriptive statistics and estimated parameters of
length-weight relationship of Indian mackerel from December 2011 to May
|*Indicates significant at p<0.01
|| Reported a and b values of different fish in different locations
|| Relationship between total length (cm) and body weight (g)
in (a) December 2011, (b) January 2012, (c) February 2012, (d) March 2012,
(e) April 2012 and (f) May 2012
Overall the sex ratio differed significantly (χ2 = 7.91; p<0.01).
Male was significantly more than female in the Indian mackerel population in
the Kuantan coastal area.
Gonadosomatic index: Monthly changes of mean gonadosomatic index (GSI)
of Indian mackerel are presented in Fig. 5. The lowest GSI
of Indian mackerel was observed in December and January. GSI of Indian mackerel
in February was higher than March and April and followed by May. GSI rapidly
increased after January and reached at peak in February (1.1958%). After February
GSI was declining again. A positive relationship was observed between GSI and
condition factor of Indian mackerel (Fig. 6).
||Monthly mean (±95% confidence intervals) condition
factor. Mean with no letter in common differ significantly (p<0.05)
||Mean condition factor (Km) per length class (total
length) for both sexes
Length-weight relationship is very useful in fisheries science for both applied
and basic use to (1) estimate weight from length observations because direct
weight measurements can be time consuming in the field (Beyer,
1987; Martin-Smith, 1996; Sinovcic
et al., 2004); (2) calculate, growth, biomass and production of a
population (Le Cren, 1951; Pauly,
1983) and (3) compare the life history of fishes of different localities
(Petrakis and Stergion, 1995); (4) determine the relative
condition of small fish compared to large fish and (5) set yield equations for
estimating number of fish landed and compare the population in space and time
(Beverton and Holt, 1957). Besides these, length-weight
relationships allow conversion of length-growth equations to weight-growth equivalents
in yield-per-recruit and related models.
The exact relationship between length and weight differs among species of fish
according to their inherited body shape and within a species according to the
condition (robustness) of individual fish (Schneider et
al., 2000). So the equation derived from the Equation logW-loga+blogL
differs every time. In the present study, the coefficient b of length-weight
relationship was ranged between 2.5128-3.0807 which was in the acceptable range
(Bagenal and Tesch, 1978).
||Monthly changes of mean (±95% confidence intervals)
gonadosomatic index (GSI) of Indian mackerel in the coastal water of Kuantan.
Mean with no letter in common differ significantly (p<0.05)
|| Relationship between GSI and Condition Factor
The b value of most fish is around 3 (Table 2) but it can
vary from 2-4 (Bagenal and Tesch, 1978). There is no previous
study in the Kuantan coastal water comparing the b value of Indian mackerel.
However, Sivadas et al. (2006) reported 3.38
as the b value of Indian mackerel in Calicut, India (Table 2).
In this study, the b-value of the LWR in April was very low (2.5128) compared
to other month. However, this might be influenced by environmental or habitat
factors. For example, differences in the water temperature, availability of
food, etc. are known to influence the growth. According to Tesch
(1971) length-weigh relationship of fish are affected by many factors including
season, habitat, gonad maturity, sex, diet, health and preservation techniques.
In this study, environmental or habitat factors were not analysed. However,
more research is needed including analyzing environmental or habitat factors
to understand the cause of low b value in April in Kuantan coastal water.
Condition factor is a quantitative parameter that indicates the state of the
fish (fatness, maturity and spawning gonadal development and general well-being
of the fish) and determine present and future population success by influencing
growth, reproduction and survival (Wootton, 1990). Condition
factor shows the populations condition (welfare) during the various stages
of the life cycle. The condition factor normally decreases at the start of the
spawning period due to very high metabolic rates. According to Mde
and Ambrosio (2002) normally condition factor increases during the reproductive
period and normalization occurs immediately after spawning. However, the study
of the condition factor is very important for understanding the life cycle including
spawning season of fish species and contributes to adequate management. In the
present study, the condition factor of Indian mackerel was lower in December
and January. Condition factor of Indian mackerel in February, March and April
were higher than the other months. Condition factor of Indian mackerel in May
was still higher than December and January. In the present study, it was also
observed that the condition factor was positively correlated with gonadosomatic
index of Indian mackerel. Based on condition factor and gonadosomatic index,
it can be concluded that the peak spawning season of Indian mackerel in the
Kuantan coastal water is from February to April. However, the spawning season
of Indian mackerel in Kuantan coastal water may fall within the period between
end of January and end of May.
This study provided a basic information on the length-weight relationship and
condition factor of R. Kanagurta that would be useful for fisheries management.
This data can be specifically used to impose adequate regulations for sustainable
fishery management in the Kuantan coastal water, Malaysia. In this study, the
b-value of the length-weight relationship of Indian mackerel in April was very
low compared to other month. This might be influenced by environmental or habitat
factors. Therefore, more research is needed including analyzing environmental
or habitat factors to understand the cause of low b value in April in Kuantan
coastal water. The peak spawning season of Indian mackerel in the Kuantan coastal
water was from February to April. The spawning season of Indian mackerel in
the Kuantan coastal water may fall within the period between the end of January
and end of May.
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