Background

The length-weight relationship is an important fishery management tool, it can be used to predict the fish weight from a known length (Pauly, 1983). The condition factor estimates the general wellbeing of fish (Abowei, 2006). Successful fisheries management and aquaculture depends on assessment of fecundity to understand the recovery ability of fish populations (Tracey et al., 2007). Gonadosomatic index and fecundity of fish are related to spawning and reproduction of fish. The gonadosomatic index (GSI) reveals the percentage of body weight of fish that is used for egg production (Fawole, 2002). The high demand for fish in Nigeria has increased pressure on the population of fish which have resulted in a decline in catches from natural habitat like Ogbese River.

Parauchenoglanis altipinnis belongs to the family Claroteidae and members are referred to as African spotted catfishes, found in fresh waters of tropical Africa (Reed et al. 1967; Froese and Pauly, 2011) where they constitute a significant component of the catches. This fish species which used to be in abundance is now scarcely found in the catches of fishermen in Ogbese River, their availability is essential being a good source of food for the poor people. Despite its wide distribution and economic value, there is dearth of information on its biology and reproductive potential. For a maximum fish yield to be obtained from a body of water using the minimum effort and without depleting adversely the available stock, knowledge of the general biology of resident fishes is fundamental (Fawole, 2002). Knowledge about the reproductive biology is also very important in determining the suitability of the species for aquaculture (Odedeyi, 2008). The present study is aimed at making investigations to the length-weight relationship, condition factor, sex ratio, fecundity and gonadosomatic index of P. altipinnis in Ogbese River, Southwest Nigeria. This may add to the limited existing information on this fish species.

1 Materials and Methods

1.1 The study area

The study was carried out in Ogbese River (Figure 1), a major tributary of Ose River in the Southwestern part of Nigeria. The river lies between longitudes 5°26’E to 6°34’E and latitudes 6°43’N to 7°17’N. It took its source from Apata Hills in Ekiti State, flows for approximately 22 kilometers from its source to meet Ose River which is about 300 km long and discharges into the Atlantic Ocean through a series of creeks and lagoons. The fishermen operate from non-powered dug-out canoes and use a variety of gears which include gill nets, long lines, traps and cast nets.

1.2 Fish sampling

P. altipinnis specimens were collected once weekly, directly from fresh landings of fishermen from Ogbese River between May 2014 and April 2015. The specimens, totaling 240, were selected randomly to include various size ranges. The specimen were sorted into two size groups namely, juveniles (<10.00 cm) and adults (>10.00 cm). Records of total length (cm) and body weight (g) measurements of individual fish were made before preserving them in ice. The specimens were dissected, sexes were noted, gonad development were assessed and classified according to Clay (1979) and matured gonads were preserved in formol-saline (4% formalin plus normal saline ratio 1:1) prior to fecundity studies. Fecundity was estimated by gravimetric method, each preserved ovary was weighed and the number of eggs from three 10 g sub-samples was counted (Abidin, 1986). The means of the total number of eggs in the sub-samples were determined while the total number of eggs per ovary was determined by the formula:

Where: F = fecundity, G = total weight of eggs, g = weight of sample eggs, n = number of eggs

2.3 Data analysis

Length-weight relationship was calculated using Le Cren (1951) equation W = aLb. The data were transformed into logarithms to determine the growth pattern thus:

Where W = body weight of fish (g), L = total length of fish (cm), a = constant, b = exponent.

The condition of the fish was expressed by Fulton’s condition factor (K), calculated using the formula (Bannister, 1976):

Where K = condition factor, W = weight in g, L = Length in cm.

The gonadosomatic index (GSI) was calculated using the formula:

2 Results

2.1 Length-weight relationship

The total lengths of 240 specimens of P. altipinnis examined in this study ranged from 12.6 to 18.8 cm while the weights ranged from 28.00 to 76.20 g. Figure 2 illustrates the length-weight relationship of the species. Table 1 presents the length-weight regression analysis of the species. Relationship between total length and body weight of all the specimens were estimated as:

2.2 Condition factor

The condition factor (K) value was calculated for P. altipinnis. The condition factor (K) for male ranged from 0.87 to 1.41 while in females it ranged from 0.85 to 1.74 and the mean condition factor for male, female and combined sexes were 1.17, 1.19 and 1.18, respectively (Table 1).

2.3 Sex ratio

The results showed that of the 240 specimens examined 116 were males and 124 were females giving a sex ratio of 1:1.07.

2.4 Gonadosomatic index (GSI) and fecundity

The gonad weight expressed as a percentage of the fish body was used as the gonadosomatic index (GSI). The GSI for male ranged from 0.12 to 2.94 while that of the females ranged from 4.75 to 40.92. The mean GSI for male was 0.52 while 14.15 was for females. In Table 2, fecundity ranged from 492 eggs (14.5 cm) to 6397 eggs (17.6 cm). The fish specimen with the lowest fecundity has a total length of 14.5 cm and body weight 33.2 g while that with the highest fecundity had total length of 17.6 cm and body weight 61.29 g. The relationships between fecundity and fish length; and fecundity and fish weight are shown in Table 3.

3 Discussion

The weight of a fish is considered to be function of its length (Zafar et al., 2003). Allen (1938) stated that an ideal fish maintains dimensional equality, the value of b would be 3.0. A value significantly larger or smaller than 3.0 indicates allometric growth (Tesch, 1978)

The length-weight relationship of P. altipinnis showed an increase in weight with a corresponding increase in length. The value of the regression coefficient (b) is 2.35 which show that the species exhibit negative allometric growth, they put on weight slower than they increase in length in Ogbese River. This value was similar to the values reported for some freshwater fish species (Thomas et al. 2003)

The coefficient of determination (r²) of 0.75 showed a positive correlation between length and weight of this fish in the river. The mean condition factor of 1.18 obtained for the population of P. altipinnis in Ogbese River was an indication of the good condition of the fish (Bannister, 1976). Fawole (2002) also reported 1.20 as the mean condition factor for M. rume in Lekki lagoon, Lagos. Mann (1980) stated that GSI is a rough measure of reproductive effort. Gonadosomatic indices ranged from 0.1 to 2.94% (males) and 4.75 to 40.92% (females) with mean 0.52%, 14.15% for males and females respectively. The high gonadosomatic indices recorded for both males (2.94%) and females (40.92%) in the months of August and September, suggests that the possible spawning period of P. altipinnis was during the rainy season, which is in agreement with Konan et al. (2014). The species was found to be of high fecundity which ranged between 492-6397 eggs per fish. The correlation coefficient (r), between fecundity and gonad weight (0.90); fecundity and GSI (0.61), were significant (p<0.05). This study has shown that there were wide variations in the fecundity of P. altipinnis, Fawole and Adewoye (1999) attributed these wide fluctuations to differential feeding success within members of the fish population. From the result of this study, P. altipinnis was in good condition and highly fecund, thus a potential candidate for aquaculture production to meet the high demand for fish in Nigeria.

Acknowledgements

I wish to express my gratitude to Mr. A. Adejuyigbe of the Department of Animal and Environmental Biology, Adekunle Ajasin University, Akungba- Akoko, Nigeria for his assistance in the collection of specimens.

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