Continental J. Biological al S Sciences 6 (3): 43 - 52, 2013 © Wilolud Journals, 2013 13 Printed in Nigeria ISSN: 21411 - 4122 http://www.wilolud ludjournal.com doi:10.5707/cjbiolsc lsci.2013.6.3.43.52 REPRODUCTIVE BIOLOGY AND ND VIRTUAL POPULATION ANALYSIS (VPA) OF Brycinus B nurse (Characiformes: Ales lestidae) IN A TROPICAL FLOOD RIVER SYSTEM Uneke Bili ilikis Iyabo1 and Nwani Christopher Didigwu2 Fisheries and Hydrobiology Unit,, D Dept. of Applied Biology, Faculty of Biological Sciences, s, Ebonyi State University, Abakaliki. 2Molecularr bi biology Unit, Dept. of Zoology and Environmental Biology ogy, Faculty of Biologica ical Sciences, University of Nigeria, Nsukka 1 ABSTRACT The reproductive biology and an virtual population analysis of Brycinus nurse were stu studied. Sex ratio was 1:1.5 for B. nurse nur (χ2 = 72.80, df = 1, P < 0.05), indicating significantly ly more females than males. Statistic stical analysis (Chi square) revealed that there were signif nificant differences in the M: F sex ratio of B. nurse in all the four gonad maturation stages, st immature stage, mature stag tage, ripe stage and spent stage. B. nurse had gonadosom somatic index (GSI) of 2.68 ± 0.199 for f males and 5.71 ± 1.28 for females with range betwee een 0.1 and 15.9. The fecundity of B. B nurse ranged from 435 to 2010 with a mean of 8833 ± 397 eggs. Fertility co-efficient (F (FC) was 0.27 ± 0.17. The smallest sexually mature fema male of B. nurse was 10.2cm TL. VPA VP revealed one peak of fishing mortality evident in the 1011cm TL length group with ith catch in number as 61220.45, survivors as 663624.26 .26 and number of recruits to fisher hery was 3318124.3. Reproduction of B. nurse populatio ation is successful and the population ion structure indicates a species that is well adapted. KEYWORDS: sex ratio, gon onad maturation, gonadosomatic index, fecundity, B. nurse se. Received for Publication: 022/08/13 Corresponding author: uneke kebij@yahoo.com Accepted for Publication: 08/12/1 /13 INTRODUCTION The freshwater fish Brycinus nurse (Or Order: Characiformes; Family: Alestidae), is a bony fish and an an important fish in the ecology of tropical waterss as a well as in the resources of aquatic systems of the sub subtropical region. This species is a native to freshwaterr ssystem in Africa thriving well in both lacustrine and rive riverine conditions (Boulenger 2002). The species is of great significance in African inland fisheries due to its abundance, widespread distribution, food and comm mmercial value (Erondu and Bowmaker 2007). The famil ily Alestidae and species Brycinus nurse reproduce heter terosexually. Usually characids have high fecundity, produ duces small sized eggs and show low or non-existing pare arental care (Saliu and Fagade 2003). Knowledge of sex distribution, dis stages of development of the gonad, size at maturity, gonado somatic index and fecundity is imp mportant in stock assessment, stock discrimination andd rrational utilization of stock (Offem et al. 2008). Studi udies on breeding seasons and factors associated with it are needed to protect new recruits and predict recruitm uitment variability (Leone 1967; Offem et al. 2008). Studi udies about fecundity of a fish are essential for evaluating ng the commercial potentialities of its stock, life history,, pr practical culture and actual management of the fishery (Lag Lagler 1956; Doha and Hye 1970). Fecundity varies from om one species to another, depending on the environme mental conditions, length, age etc (Musa and Bhuiyan 2007 007). Furthermore the knowledge of fish fecundity is needed ded in establishing its production potential and consequen uently its exploitation and management rationale (Fawole ole and Arawomo 2000). Knowing the age of first spawn wning and the age of fish being caught is an importantt aaspect of fishery assessment (Fawole and Arawomo 200 000). Fisheries management should consider the values of basic biological parameters of the fish from various wate ater bodies including their reproductive potential. Thus this his article seeks to study the reproductive biology of B. nurse nu and provide information on the sex ratio, variation in the percentage male and female of B. nurse at each maturation m stage, the gonadosomatic index, absolute, rela elative fecundity), recruitment pattern and the virtual popu pulation analysis of B. nurse. All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 1 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 MATERIAL AND METHODS Study area The study was carried out in the Cross ss River which is a major component of the inland waters rs of o south-eastern Nigeria and its role to the fishery of the area is quite significant (Okoh et al. 2007). Cross River er originates from Cameroon and flows through Ebonyii State S and Cross River State of Nigeria, into the Atlanticc Ocean. O The river lies in the area between 5057” - 5030’20 ’20” N and 7058” - 5030’20” E (Okoh et al. 2007). The appr proximate surface area of the Cross River is 3,900,000 ha (Ita et al. 1985) (Fig. 1). The rainy season and the dry sea season are the two main seasons of the area. The dry seas eason occurs between October and November - March, while wh the rainy is from April - September and October.. D During the rainy season, water level increases drastically ly iin the river. The rise in water levels of the river is broug ught about by direct precipitation within the catchments areas are as well as by inflow from the Afikpo and Cross Riv iver flood plains. The inundated soils are composed off sandy sa with good water retention capacity. During the dr dry season, water level is restricted to the main river cha channel and some flood plain pools (Okoh et al. 2007). ). A summary of the physicochemical variables of the Cr Cross River is as shown in Table 1, with higher values es of pH, dissolved oxygen, conductivity, total dissolved ved solids (TDS), temperature and phosphate in the dry se season while nitrate was higher in the rainy season (Okogw gwu et al. 2011). Fig. 1: Map of Afikpo North Local Gov overnment Area showing the sampling locations in the Cross Cr River basin (Okoh et al., 2007). Table 1: Summar ary of physicochemical variables of the Cross River. Dry season Wet season Mean ± SE Mean ± SE pH 6.8 ± 0.2a 6.9 ± 0.3a Dissolved oxygen (mg/l) 6.7 ± 0.8a 4.7 ± 0.9ab Conductivity (µS) 40.3 ± 7.0a 26.2 ± 3.5ab TDS (mg/l) 19.0 ± 3.6a 11.5 ± 1.9a Temperature (oC) 32.0 ± 2.0a 28.0 ± 1.8b 0.82 ± 0.5a 0.9 ± 0.5a NO3 (mg/l) PO4 (mg/l) 1.1 ± 0.4a 0.7 ± 0.4a * – values in the same row with simila ilar letters are not significantly different (p > 0.05) (Okogw gwu et al. 2011) All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 2 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Sample collection The study was carried out on B. nurs urse population from Cross River basin South-eastern Nigeria. Ni The fish samples were collected each month fro from four sampling locations, Ozizza, Ndibe, Enohia and Uwana in the Cross River basin at Afikpo, Nigeria (Fig. (F 1). Monthly samplings were made by random samples les of the catch of the commercial artisinal fishers usingg ggillnets with various mesh sizes (18-55 mm), cast nets, s, lift l nets, fishing baskets and traps between January 2010 20 and July 2011 and a total number of 1820 of the he specimen were sampled. Laboratory analysis The samples were sorted and identified fied to species level using the guides of Olaosebikan andd Raji R (1998). Sex determination, gonad maturation stagee aand fecundity were done through examination of the inte nternal sex organs. The sex and the stages of developmen ent of the gonad were determined by visual inspection aand graded. The surrounding ovarian tissues were remooved and the number of eggs in each pair of ovaries was as determined by direct enumeration (Ezenwaji and Offia ffiah 2003). Fecundity was also studied by gravimetric method me (Hunter et al. 1989). The procedure is as follows; s; the subsamples of 1 or 2 g according to the size of thee eggs e were taken from the front, middle and back parts ts of o the ovaries. The number of the sub-samples was mult ultiplied up to the weight of the ovary. Total length (TL) L) and Standard length (SL) were measured to the neares rest 0.1cm with a meter rule measuring board. Weight measurements me were made with a FEJ-1500A electronic compact com weighing balance to the nearest 0.1g. Fishh samples were preserved in 10% formalin as vouc ucher specimens (UBI/PhD/B.nurse/2011) in the laborato atory of Applied Biology Department, Ebonyi State Univers ersity, Nigeria. Data analysis The FAO-ICLARM Fish Stock Asses sessment Tools (FISAT II) software (Gayanilo et al. 200 005) was used to construct length-frequency distribution on table for the species population to determine the domina inant size group(s) and their percentage composition. Mea ean values of length and weight measurements were deter etermined. Overall sex ratio and heterogeneity significance ce were determined with the use of Chi square statistical analysis. an Gonad maturation was evaluated macr acroscopically and categorized into four maturation stages ges (Ezenwaji and Offiah 2003) as follows: Immature stag stage (stage I), Mature stage (stage II), Ripe stage (stagee III), I Spent stage (stage IV). Chi square statistical analysi ysis was used to determine the significance difference in the sex ratio in all the stages. Relative gonadosomatic index (GSI ) was wa estimated according to De Vlaming et al. (1982) as: GSI SI = Gonad weight/Body weight × 100 Fertility coefficient (FC) was estimated ed according to the equation of Riedel (1969): FC = E/TL3 where E = number of eggs produced and TL = total length of female fish (cm). Nikolsky (1969) described the relationsh nship between fecundity and total length and weight as: F = aT aTLb, F = aSLb, F = aGW b and F = aWT b where F = Fecundity TL = Total length (cm (cm) SL = Standard length gth (cm) GW = Gonad Weight ght BW = Body Weight b = Slope of the reg regression line (regression coefficient). a = Intercept of the regression with the y - axis (regression constant). Regression analysis was used in the esti estimation of the a and b values and the level of significance nce of the value of co-efficient of correlation (r) using FISA ISAT II. All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 3 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 vely as: The length (lm) (Roff 1986) and age (tm) (Roff 1984) at sexual maturity was estimated respectivel l m = L∞ [3k (3k + m) ] t m = ( 1 ) ln (3k + m) / m k where lm = length at sexual maturity L∞ = asymptotic length of fish K = growth curvature parameter m = natural mortality tm = age at sexual maturity Virtual population analysis (length struc ructured VPA) is methods which allow the reconstruction of the population from total catch data by age or size. The he initial step is to estimate the terminal population (Nt) given giv the inputs, from Nt = Ct · (M + Ft)/Ft where Ct is the terminal catch (i.e., thee ccatch taken from the largest length class). Then, starting from Nt, successive value lues of F are estimated, by iteratively solving, Ci = Ni+t · (Fi/Zi) · (exp (Zi·ti)-1) where ti = (ti+1 - ti), and ti = to - (1/K) · ln(1-(Li/L)) and where population sizes (Ni) are com omputed from Ni = Ni+t · exp (Zi) The last two equations are used altern ernatively, until the population sizes and fishing mortality lity for all length groups have been computed. An F--array representing the fishing mortality for each length len group, the reconstructed population (in numbers), ), and a the mean stock biomass by length class were made us using FISAT II. RESULTS Size composition In the length-frequency of the 1820 B. nnurse the smallest and largest specimens were 6.3cm TL L and 22.8cm TL respectively (mean = 12.8 cm ± 0.91) 1) (Fig. ( 2). The 9 to 12cm TL size ranges were numericall ally dominant and constituted 52.3% of the catch. Modal al length class was 10-11cm TL (Fig. 2). The weight rang nged between 7.0 and 210.3g (mean = 129g ± 10). Sex ratio In relation to variation in sex ratio with ith length class, females dominated markedly at 18-19 cm TL T (m: f = 1:1.8) and from 19-23 cm TL length class (Fig. (F 3) while variation in sex ratio with the months show owed that females dominated markedly in May 2010 (m:: f = 1:1.8), May 2011 (m: f = 1:1.8) and June 2011 (m:: f = 1:1.8) (Table 2). The overall monthly sex ratio (M:: F) was significantly different 1:1.5 (χ2 = 72.80, df = 1, P < 0.05) (Table 2). Females dominated considering the wh whole 18 months and there was significant heterogeneity (χ2 = 82.06, df = 17, P < 0.05). There were more female ales than males in both the dry (male = 295, 42.6%; female ale = 397, 57.4%; sex ratio 1:1.3; χ2 = 7.52, df = 1, P < 0.0 0.05) and the rainy seasons (male = 433, 38.4%; female = 695, 6 61.6%; sex ratio 1:1.6; χ2 = 60.85, df = 1, P < 0.05). 5). All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 4 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Fig. 2: Length-frequency distribution of male and female of B.nurse from January 2010 to Junee 2011 2 in the mid Cross River basin, Nigeria. Fig. 3: Variation in sex ratio with (lengt ngth class) size of B. nurse, January 2010 through June 2011 11 in the mid Cross River basin, Nigeria. Table 2: The monthly sex ra ratio (M : F) of B. nurse in the mid Cross River basin, Nige igeria. Month Nu Number sampled Sex ratio Male Female Total M:F Calcula ulated χ2 38 69 1:1.2 0.7 0.71 JAN. 2010 31 FEB. 2010 38 53 91 1:1.4 2.4 2.47 MAR. 2010 31 47 78 1:1.5 3.2 3.28 APR. 2010 42 67 109 1:1.6 5.7 5.73 MAY. 2010 41 72 113 1:1.8 8.5 8.50 JUN. 2010 44 76 120 1:1.7 8.5 8.53 JUL. 2010 51 86 137 1:1.7 8.9 8.94 AUG. 2010 42 63 105 1:1.5 4.2 4.20 SEP. 2010 43 60 103 1:1.4 2.8 2.80 OCT. 2010 51 60 111 1:1.2 0.9 0.93 NOV. 2010 55 62 117 1:1.1 0.4 0.42 DEC. 2010 38 54 92 1:1.4 2.7 2.78 JAN. 2011 34 44 78 1:1.3 1.2 1.28 FEB. 2011 29 41 70 1:1.4 2.0 2.06 MAR. 2011 39 58 97 1:1.5 3.7 3.72 APR. 2011 40 68 108 1:1.7 7.2 7.26 MAY. 2011 35 63 98 1:1.8 8.0 8.00 JUN. 2011 44 80 124 1:1.8 10.4 0.45 TOTAL 728 1092 1820 1:1.5 72.8 2.80 RAINY SEASON 295 397 692 1:1.3 7.5 7.52 DRY SEASON 433 695 1128 1:1.6 60.8 0.85 Data obtained from periodic observation tions made on 1820 specimens from January 2010 through h JJune 2011. All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 5 P 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Gonad maturation Four maturation stages were encountere tered; immature, mature, ripe and spent stages. In the male ales, 30.4% of the total fish sampled were at the immature ture stage. The mature stage was 32.7%, 34.2% were in the ripe stage and 2.7% were in the spent stage indicating ng 69.9% were in the reproductive process. Female’s popula ulation had 22.7% in the immature stage, 49.5% in the ma mature stage, 25.3% in the ripe stage and 2.5% in the spen ent stage showing 74.8% were in the reproductive process. ss. There were significant differences in the M: F sex ratio io iin all the stages; immature stage (χ2 = 1.55, df = 1, P < 00.05), mature stage (χ2 = 117.85, df = 1, P < 0.05), ripe stage st ((χ2 = 1.39, 2 df = 1, P < 0.05) stage and spent stagee (χ = 1.04, df = 1, P < 0.05) (Table 3). Highest percentage ge of females was in the mature stage (1:2.3) while thee lowest percentage of females was in the ripe stage (1 1:1.1) (Table 3). Smallest mature male and female B. nu nurse sampled were 8.7 and 10.2 cm TL respectively. The he median size at maturity for B. nurse for both sexes was as 12.23 cm TL which is 52% of its asymptotic length (23. 23.63 cm TL). The median weight at maturity for both se sexes was 128.21g which is 53.6% of its asymptotic weight w (239.1g). Estimated values of lm and tm were 12.62 .62 cm TL and 0.62 yr respectively. Table 3: Maturation stages dynamics of male and female B. nurse from mid Cross River basin,, Nigeria. N Maturation No (%) of No (%) of Sex ratio Calculated χ2 P Stage Male Female M:F Immature 221 (30.4) 248 (22.7) 1:1.1 1.55 0.05 Mature 238 (32.7) 541 (49.5) 1:2.3 117.85 0.05 Ripe 249 (34.2) 276 (25.3) 1:1.1 1.39 0.05 Spent 20 (2.7) 27 (2.7) 1:1.4 1.04 0.05 Total 728 1092 1:1.5 72.80 0.05 Data obtained from periodic observation tions made on 1820 specimens from January 2010 through h JJune 2011. Gonadosomatic index (GSI) B. nurse had gonadosomatic index (GSI SI) of 2.68 ± 0.19 for males and 5.71 ± 1.28 for females wi with range between 0.1 and 15.9. Monthly variation tions in GSI of both sexes followed nearly the same pattern. rn. Higher GSI values occurred during the period from m March to August with a peak in July, while the lower one nes occurred during the period from September to Fe February (Fig. 4). The females had higher GSI over males es (Fig. ( 4). Fig. 4: Monthly gonadosomatic index of B. nurse from January 2010 to June 2011 in the mid Cross River basin, Nigeria. Fecundity The fecundity of B. nurse ranged from m 435 (8.4 cm TL, 30.8 g) to 2010 (18.0 cm TL, 115.6 g) with a mean of 883 ± 397 eggs. Fertility coefficient (FC) (FC was 0.27 ± 0.17. Highest and lowest FC values were re in females with 8.4 cm TL, 435 eggs (0.73) and 22.8 cm TL, 880 eggs (0.07) respectively. Fertility coefficientt did d not have any correlation with the length. Fecundity ty was positively correlated with total length (TL), standa dard length (SL), body weight (BW), and gonadal weigh ight (GW) (Table 4). It is worthy to note that fecundity vvaried with total length by a factor of 2.19 and standardd llength of 2.23 (Table 4). All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 6 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Table 4: Functional equation showingg th the relationship between fecundity (F) and other variables es of B. nurse in the mid Cross River basin, Nigeria. Correlation coeffient (r) r2 p Functional equation (F = a X b) 2.19 F = 1.958 (TL) 0.955 0.911 0.0 0.05 F = 2.781 (SL)2.23 0.933 0.870 0.0 0.05 F = 1.896 (BW)1.45 0.967 0.934 0.0 0.05 F = 22.131 (GW)1.86 0.788 0.621 0.0 0.05 Key: TL = Total length, SL = Standard rd length, TW = Total weight, OW = Ovarian weight. Data obtained from periodic observation tions made on 1820 specimens from January 2010 through h JJune 2011. Virtual Population Analysis (length structured str VPA) The results of the length structured VPA PA analysis of B. nurse are shown in Fig. 6. One peak of F is evident in the 10-11cm TL length group. F was 1.677 w with catch in number as 61220.45, survivors as 663624.26 .26. Number of recruits to fishery for B. nurse was 3318 18124.3. Fig. 6: Length structured Virtual Popula ulation Analysis of B. nurse in the mid Cross River basin,, Nigeria. N DISCUSSION as 1820 with the length size of 6.3-22.8cm TL. Length groups gro 9-12cm TL Total number of B. nurse samples was were numerically dominant and constitu tituted 52.3% of the catch with one mode at 10-11cm TL le length class. This corresponded with the VPA results whi hich showed the peak of fishing mortality (F) in the length gth class 10-11cm TL. According to Ikomi and Sikoki (20 (2001), the combined length frequency distribution of B. nurse nu in the River Jamieson, Nigeria, showed that the pop opulation structure consisted of two distinct length classes ses of 7.0-13.9 cm and 14.0 cm and above. The modal leng engths were between 10.0 and 11.0 cm for the males and 11.0 11 and 13.0 for the females in the medium size groupp ((MSG) or young adult (7.0-14.0cm TL) which are in line ine with the modal length class (10-11cm TL) of this study dy. The monthly variation in the length frequency distribut ution showed that fish of both MSG and LSG (least size ze group) were encountered in the river. This was in acco cordance with the modal length of fish in this study (10 10-11cm TL). However, the length frequency distribution ion pattern of the length groups was not leptokurtotic. In the B. nurse population studied, ther here were significantly (P < 0.05) more females than males les (M:F = 1:1.5). This agreed with the report on B. nu nurse in Asa reservoir, Ilorin, Nigeria where a female le dominance was observed within the population, withh a sex ratio of 1.0 male to 1.78 females (Saliu and Fag agade 2003). The findings of Offem et al. (2009) was in contrast c with the sex ratio of M:F = 1:1 for Alestes nurse rse in Cross River inland wetlands, Nigeria. The preponde derance of the female over the male as observed in this stud tudy had similarly been observed by Paugy (1980) in po populations of the species from four basins in Ivory Coa oast. Ham (1981) attributed these disparities to differenti ntial survival over certain environmental conditions, whil hile Fagade et al. (1984) explained the phenomenon ass a mechanism for population regulation. However, the preponderance pr of females can also be attributed to the fac fact that male B. nurse has been known to carry out migrat ratory movements prior to spawning and such a phenomen enon has been documented by Whitehead (1959) and Reyno ynolds (1973). All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 7 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Migratory movements of males priorr to spawning can not be ascertained in this study, but female fem dominance agreed with the phenomenon as a mech echanism for population regulation in terms of the genetic tic factor set-up to ensure constant and continuous procrea eation for the regeneration and sustenance of the stock. nurse in this study showed that 69.9% of the males were in the t reproductive Data on the gonad maturation of B. nur process while 74.8% of the female population po were in the reproductive process. Smallest m mature male and female B. nurse sampled were 8.7 andd 110.2cm TL, respectively, indicating that males reach mat aturity before the females. B. nurse had gonadosomaticc index i (GSI) of 2.68 ± 2.19 for males and 5.71 ± 5.288 for fo females with range between 0.1 and 15.9. Monthlyy variations v in GSI of both sexes followed nearly the samee pattern. Higher GSI values occurred during the periodd ffrom March to August with a peak in July, while the lowe wer ones occurred during the period from September to February. The period with higher GSI (March - August) A may be representing the spawning season. Analysis An of the frequency distribution of the maturation on stages and the average monthly values of GSI, showin ing the presence of ripe stages in the ovary throughout the he year, indicate a polycyclic breeding habit for B. nurse.. According to Saliu and Fagade (2003), the GSI of bothh male m and female B. nurse in Asa reservoir ranged from m 0.02 -29.25% with a mean value of 6.43 ± 0.39. Thee low GSI values obtained for B. nurse in Asa reservoir ir were after the peak spawning period which could be as a result of the frequency of spawning. It was observ erved that an increase in the frequency of spawning in fish is usually accompanied by a fall in G.S.I. The months mo of peak spawning corresponded with the on set off the th rains and the floods. The finding of this study agreed eed with the above reports. Breeding of tropical species att tthe beginning of the rainy season has been observed and that most tropical fishes are adapted to breed on thee rising r flood thus allowing the juveniles to take full adva vantage of the flooded banks for feeding while protected ed from predation. The choice of a particular season in fishes fis for breeding is influenced by various factors among ong which is food supply, changes in water quality or le level, interspecific interactions, availability of spawning ng sites (Harding, 1966; Offem et al. 2008). According to Wootton (1995) and Low owe-McConnell (1987), exogenous ones such as photoperio riod, temperature, water flow and level and precipitation, on, can serve as triggers for tropical fish reproduction. In this study, GSI values were higher during the wet et season (March-August) than the dry season (Septem tember-February). Significantly lower values of dissolved ed oxygen, conductivity and temperature favoured the hig igher GSI values while lower values of TDS AND PO4 w were unrelated to the higher GSI values. Also the higherr values v of Ph and NO3 were unrelated to the higher GSII va values during the wet season. Adebisi (1987) reported that Characid cids, Cyprinids, Schilbeids and Mochokids produce comp mparatively small sized planktonic eggs because they are highly fecund and show little or no parental care. The he fecundity of B. nurse in this study ranged from 435 to 2010 with a mean of 883 ± 397 eggs which was not in agreement with Saliu and Fagade (2003), that reported ed absolute fecundity estimates of B. nurse to ranged from om 1,720 - 68,700 eggs with a mean of 18,281 eggs, while ile the relative fecundity estimates ranged from 19,933 to 849,453 8 eggs /kg of body weight, with a mean of 345,00 000 eggs/kg of body weight. The high absolute fecundity ity recorded by B. nurse in Asa reservoir is typical of pel pelagic fishes. For the Asa reservoir population of B. nurse rse, the small egg size, lack of parental care within the he species and availability of food were factors implicat cated for its high fecundity. Relatively low fecundity of this study may be related to lack of parental care exposing ex eggs to predators. Cross River basin is a lotic tic water system known to be rich in species composition on with predatory species (Okoh et al. 2007) which could uld take advantage of the planktonic eggs. It is worthy to note n that in this study, fecundity varied with total length gth by a factor of 2.19 and standard length of 2.23, indicatin ting that fecundity approximate the square of the body len length. The use of fish weight to determine the fecundity sh should be treated with caution since somatic weight chan hanges near the spawning period and introduces some erro rrors. Calculations with total length instead of standard leng ength may cause slight differences in the values. The length-structured VPA is a powerfu rful tool for stock assessment by which the size of each coh cohort is estimated alongwith the annual mortality causedd bby fishing. The highest peak of F (1.67) was evident inn tthe 10-11cm TL length group which might be associated ted with the use gillnets with various mesh sizes (18-55 mm mm), cast nets and lift nets used by the artisinal fishers in tthe river system. Catch in number was 9.2% (61220.45) 5) of the survivors indicating a stable and viable population tion. All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 8 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 These findings on population of this species spe at Cross River basin confirmed that there are regiona onal differences in the reproductive dynamics of B. nurse as found in other fish species (Bagenal 1978). In this stud tudy, reproduction of B. nurse population of the Cross R River is successful and the species, well adapted, therefo efore can provide excellent broodstock. Since smaller fish in this population dominated, the smaller fish should ld be b used for fish conservation. REFERENCES Adebisi AA. 1987. The relationship bet between fecundities, gonadosomatic indices and egg sizess oof some fishes in Ogun River, Nigeria. Arch Hydrobiolog logia 3(1): 151-156. Bagenal TB. 1978. aspect of fish fecundity, fec pp 75-101. In S.D. Gerking (ed.) ecology of freshwater fish reproduction. Blackwell Scientific Publi blications Oxford. Brycinus species from the lekki lagoon, Lagos State, Nigeria. Ni Nigerian Boulenger DP. 2002. The biology of B Journal of Science 12: 73-84. De Vlaming V, Grossman G, Chapman an F. 1982. On the use of gonadosomatic index. Comparativ ative Biochemistry and Physiology 73: 31-39. Doha S, Hye MA. 1970. Fecundity off the th Padma river Hilsa ilisha (Ham.). Pakistan Journal off Science S 22: 176183. Erondu ES, Bowmaker AP. 2007. Thee diet d of wild and pond cultured African tetras in mangrove ove swamps of the Niger Delta, Nigeria. Journal of African can Zoology 104: 367-371. Ezenwaji HMG, Offiah FN. 2003. 3. The biology of Pellonula leonensis Boulenger, 1916 16 (Osteichthyes: Clupeidae) in Anambra River, Nigeria. a. Journal of Biological Research and Biotechnology 1 (2): ): 33-50. Fagade SO, Adebisi AA, Atanda AN.. 11984. The breeding cycle of Sarotherodon galilaeus in th the I.I.T.A Lake, Ibadan, Nigeria. Arch. Hydrobiologia 10 100 (4): 493- 500. Fawole OO, Arawomo GAO. 2000. 0. Fecundity of Sarotherodon galilaeus (Pisces: Cichlida lidae) in the Opa reservoir, Ile-Ife, Nigeria. Revista de Biologia Bio Tropical 48: 1-6. Ham R. 1981. The ecology of six nativ tive and two introduced fish species in Enoggera creek syst ystem, South east, Queens land. Bsc. (Hons) Thesis. Griffi iffith Univ. Brisbane. Harding D. 1966. Lake Kariba: the hyd ydrology and development of fisheries. In Manmade lakes. es. 2 nd edn. (R.H. Lowe Mc 25. Connel ed.). Academic pr press, London. pp: 123-134. Hunter JR, Macewicz BJ, Kimbrell CA CA. 1989. Fecundity and other aspects of the reproductio ction of sablefish, Amploporna fimbria, in Central Californ ornia waters. CalCOFI Report 30: 61-72. Ikomi RB, Sikoki FD. 2001.Studiess on the distribution, abundance, growth pattern and dietary di habits of Brycinus nurse Ruppel, 1832 (Osteich ichthyes: Characidae) in the River Jamieson, Nigeria. Acta Ac Ichthyologia Piscatoria 31(1): 27-44. Ita EO, Sado EK, Pandogari JKA, Ibito itoye B. 1985. Inventory survey of Nigerian inland waters rs and a their fishery resources I. A preliminary checklist of inland water bodies in Nigeria with special referencee to t ponds, lakes, reservoirs and major rivers. Kainji Lake ake Research Institute Technical Report Series, No. 14, KL LRI, New Bussa, 1-51. Lagler KF. 1956. Ennumeration of fish eggs. In freshwater fishery biology. 2nd Edn. W.M. Brown B company publishers. Dubuque: 106-110. All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 9 Uneke Iyabo and Nwani Did idigwu: Continental J. Biological Sciences 6 (3): 43 - 52,, 2013 2 Leone CC. 1967. Fecundity of surf sm smelt in the state of Washington. M.Sc. Thesis University ty of Washington, Seattle. Lowe-McConnell RH. 1987. Ecologic gical studies in tropical fish communities. Cambridge University U Press, Cambridge, England. 382. Musa ASM, Bhuiyan A. 2007. Fecundi ndity on Mystus bleekeri (Day, 1877) from the River Padm dma near Rajshahi City. Turkish Journal of Fisheries andd A Aquatic Sciences 7: 161-162. Nikolsky GV. 1969. Theory of Fish Pop opulation Dynamics. Otto Science Publishers, Koenigstein. in. Offem BO, Ayotunde EO, Ikpi GU. 2008. 20 Dynamics in the reproductive biology of Heterobra branchus longifilis Val, (Pisces: 1840) in the inland we wetlands of Cross river, Nigeria. Research Journal of Fisheries and Hydrobiology 3(1): 22-31. Offem BO, Samsons YA, Omoniyi IT. T. 2009. Length-weight relationship, condition factor and sex s ratio of forty six important fishes in a tropical floodd rriver. Research Journal of Fisheries and Hydrobiology 4(2): 4( 65-72. Okogwu OI, Ani CO, Uneke IB. 2011. 1. Distribution of Procamallanus laevionchus in relation to environmental variables in three tropical African river vers: The role of the host and ecosystem. Acta Zoologicaa L Lituanica 21(2): 145-152. Okoh FA, Eyo JE, Ezenwaji HMG. 20 2007. Species composition and abundance of castnet fishe shery of a tropical lotic freshwater ecosystem. Bio-Researc arch 5(1): 201-206. Field guide to Nigerian freshwater fishes. Federal Colleg lege of Freshwater Olaosebikan B.D. and A. Raji, 1998. F Fisheries Technology, New Bussa, Nige igeria. Pp. 92. Paugy D. 1980. Ecologie ET biologie ie des d Alestes nurse (Pisces Characidae) des rivieres de Cote Co d'Ivoire. Cah O.R.S.T.O.M. ser Hydrobiologia 13(3-44): 143-149. Reynolds JD. 1973. Biology and fisher hery potential of four species of Alestes (Pisces, Characini inidae) in the new Volta Lake, Ghana. Rev. Zool. Bot. Afri fri. 8(2): 298 - 310. Riedel D. 1969. Some remarks on the he fecundity of Tilapia (T. mossambicus) and its introduct uction into middle Central America (Nicaragua) together er with a contribution towards limnology of Nicaragua. Hydrobiology Hy 25: 357-388. Roff DA. 1984. The evaluation of lif life history parameters in teleosts. Canadian Journall of Fisheries and Aquatic Science 41:989-1,000. Roff DA. 1986. Predicting body size with w life History models. Bio Science 36 (5): 316-323. Saliu JK, Fagade SO. 2003. The Repro productive Biology of Brycinus nurse (Paugy 1986), Pisces ces: Characidae in Asa Reservoir, Ilorin, Nigeria. Turkish sh Journal J of Fisheries and Aquatic Sciences 3: 5-9. Whitehead PJP. 1959. The anadromous us fishes of the Lake Victoria. Rev. Zoon. Bot Afri. Lix 34, 4, 329-363. Wootton RJ. 1995. Ecology of teleostt fishes. fi Chapman & Hall, London, England. 404 All rights reserved This work by Wilolud Journals iss li licensed under a Creative Commons Attribution 3.0 Unpor orted License 10