Broodstock size combination in artificial spawning of cultured Clarias gariepinus

G A Ataguba, S G Solomon and M C Onwuka

Department of Fisheries and Aquaculture, University of Agriculture Makurdi, Nigeria
gabynotepad@yahoo.co.uk

Abstract

The experiment was aimed at determining the effect of varying brood stock weight in crosses on fecundity, fertilization and hatchability of Clarias gariepinus under hatchery conditions. Broodstock used for the present study were obtained from a homogenous source (Age: One year and three months). Combinations of broodstocks used for the study were within size ranges: 200-300g (A), 400-500g (B), 600-700g (C) and 800-900g (D).

It was observed that broodstock combination involving D females had the highest fecundity (61700.0 - 74100.0), fertilization (77.3% - 83.7%), and hatchability (74.4% - 88.7%). Of all the crosses, smaller size homogeneity did not favour fertilization and hatchability. D x D had the best hatchability (88.7%). Generally, the study observed that fecundity, testes mass, fertilization, and hatchability increased significantly as the size of broodstock increased. Therefore for better hatching success in induced breeding of Clarias gariepinus, larger broodstock are advised to be used.

Key words: egg weight, fecundity, fertilization, hatching, testes weight

Introduction

Recent trends all over the world, point to a decline in landing from capture fisheries, an indicator that fish stocks have approached or even exceeded the point of maximum sustainable yield. Aquaculture therefore remains the only viable alternative for increasing fish production in order to meet the protein need of the populace. The growth of aquaculture lies in the ability of the hatcheries to be able to produce and supply fish seeds for stocking production ponds on a sustainable basis (Bamimore 1994). The steadily growing importance of fish farming has compelled improvements in the technologies necessary for securing the initial and basic requirements for productive aquaculture; namely the production of fish seed for stocking.

In Nigeria, the major family of catfish that is of commercial interest is the family Claridae. Clarias gariepinus is mostly farmed due to its fast growth rate and ability to tolerate wide range of temperature, low dissolved oxygen, and salinity. It hardly reproduces in captivity, However, break-through have been recorded in the artificial propagation of these catfish seeds using different techniques which permit spawning, incubation, hatching of eggs and rearing under controlled environment (Eyo 2002). Artificial propagation methods constitute the major practicable means of providing enough quality seed for rearing in enclosures such as fish ponds, reservoirs and lakes (Charo and Oirere 2000). Fish seed production efficiency of many fish farms’ hatcheries throughout sub-Saharan Africa or developing countries like Nigeria is mostly low due to poor handling of brood stock (Aiyelari et al 2007).  Many hatcheries in Nigeria are facing the problem of poor spawning and low hatchability of C. gariepinus although it is widely cultured in Nigeria. Poor egg quality and low hatching rates are amongst the difficulties most often reported by fish farmers (Adewumi and Olaleye 2011). Fertilization, hatching and early survival of larvae are vital for successful aquaculture of the African catfishes (Haniffa et al 2000) and this has been investigated earlier (Ataguba et al 2009). Proper handling and health status of female brood fish has been reported to be of great importance in the reproductive performance of fish (Muchlisin et al 2006; Aiyelari et al 2007). Generally research studies had focused on hatching success in relation to environmental variables such as temperature (Oyelese 2006), and CaCO₃ water hardness (Silva et al 2003). A small but sexually matured fish is an indication of either genetic inheritance or nutritional deficiency. Size is directly proportional to fecundity and egg size (Bromage and Roberts 1995). There is a need to investigate the effects of brood stock size combination on reproductive performance given the fact that differences occur in brood stock characteristics as regards gamete production and size.

Materials and Methods

Fish origin and maintenance

Broodstock of approximately one year three months old were obtained from the Fisheries research farm of the University of Agriculture Makurdi. The broodstock were separated by sex and weight and maintained for two weeks in concrete tanks at the Hatchery Unit of the Department of Fisheries and Aquaculture, Makurdi. They were fed daily with 35% crude protein pelleted feed administered at 5% of the biomass.

 

Hormonal treatment, artificial fertilization of eggs and hatching rate

 

 Broodstock combination used for the study is shown in Table 1 above. Ovaprim was used as the hormone for inducing ovulation at a dosage of 0.5ml.kg-1 of body weight. Hormone administration was carried out via intramuscular injection without anesthesia. After a latency period of twelve hours, the eggs were collected from each female according to the designated crosses by gently pressing the abdomen of the fish. These were collected into clean bowls labeled accordingly. The weights of the egg were determined as well as fecundity. Milt was obtained by sacrificing the males. The testes were obtained according to the combination and used to fertilize the eggs accordingly. The stripped eggs were mixed with the milt gotten from the male of appropriate combination after which 5 ml of fresh water was added. After gentle and thorough stirring, the eggs were transferred and incubated in duplicate 60L capacity plastic aquaria using nylon type mosquito mesh netting as substrate in 50 litres of fresh water according to the originally predetermined combination. Eggs were incubated in this static condition with aeration at an ambient temperature between 27 to 29°C. Hatching was observed to be complete between 24 to 28 h after fertilization, and the hatching rates were evaluated about 32 hours post fertilization.

 

Determination of fertilization and of hatching rate

A known mass of egg that was not inseminated was used to determine fertilization. The time taken for these control eggs to become opaque (dead eggs) was noted, after which the brownish/greenish eggs in the incubation tanks were termed as fertilized. The number of eggs spawned was calculated by weighing 1g of eggs from each female (Triplicate determinations were made). The number of eggs in one gram was determined by counting and the average of the three counts was taken as the number of eggs in 1g of eggs. The total weight of eggs spawned for each female was noted and this was multiplied by the average number of eggs already determined in the present study.  Fertilization rate was determined using the method described by Ella (1987). A 300mm long glass tube with a diameter of 2.5mm was dipped into the egg mass while keeping the upper end closed with the thumb. The thumb was lifted and eggs were allowed to fill the tube. Representative samples were taken from the surface, middle and bottom of the fertilized egg mass. The glass tube was raised up against light and the total numbers of good and bad eggs were counted. The good (fertilized) eggs were shiny and their contents were clear as against the opaque and white appearance of bad (unfertilized) eggs. This was then used to estimate the number of bad eggs in each cross using simple proportion.

                                  

Where (N) represents the total number of eggs spawned, (b) number of bad eggs and can be obtained from the relation below; 

where (x) is the total number of eggs in the three representative samples and (y)  is the number of bad eggs counted, Hence number of good eggs (g) is denoted using:

 

The hatching rate of each cross was evaluated 32 hours after fertilization. The number of hatched larvae was determined using the volumetric method as described by Ella (1987). Three hundred larvae were counted using a fine mesh dip net and placed in a graduated measuring cylinder already filled with known volume of water with care being taken to avoid adding extra water along with the larvae. The change in water level after adding the larvae was noted. Afterwards, all the larvae were placed in a graduated measuring cylinder and the level of water change recorded. The total number of larvae in each case was determined using the equation:

                       

Data collected were analyzed using Genstat Discovery edition and Minitab 14. Fecundity, fertilization and hatching rates of the different treatments were compared using one-way ANOVA followed by Fisher’s LSD to determine significant differences among means. Percentage hatchability was subjected to Analysis of Co-variance (ANCOVA) using fertilization as covariate and means were adjusted for covariate effect.

Results and discussion

The result of the present study as shown in Table 2 shows that the different brood stock size combinations affects all the parameters measured.  Egg weight increased significantly from the lighter female to the heaviest with the highest weight of 1.58 x10-3 mg, however, eggs from the 16th , 13th , 10th , and 7th combination were comparable to each other also combination 15, 12, 11 and 9 were statistically same. In many fish species, larger females often produce larger eggs and egg mass decrease with each progressive batch through spawning (Marteinsdottir and Begg 2002 and Rideout et al 2005). This phenomenon has also been demonstrated in other Clariid species (Rijnsdorp 1991). However, Bromage and Cumaranatunga (1988) reported that increase in egg number with age is due to increase in fish size. Testis weight showed a constant trend of increase from lighter to heavier brood stocks. Fish generally need energy for growth and reproductive activity, however in cannibalistic species like Clarias, avoidance of predation make less energy available for weaklings to take care of growth and reproductive needs, hence smaller, fishes carries smaller testis compared to bigger fishes of the same age.

According to Duarte and Araujo (2002), studies on fish fecundity is important to evaluate the reproductive potentials of the species, in the present study, fecundity generally increased as the female increased with values ranging from 20500 in female from (A) group to 74100 in female from (D) group. According to Bagenal (1978) fecundity is the number of vitellogenic oocytes in mature females prior to the next spawning season (only the ripe spawnable eggs > 1.0 mm in the ovary of the fish).  Fecundity can also encompass all available eggs in the ovary of the brood stock following authors such as Clay (1979), Eyo and Mgbenka (1992), and Ezenwaji (1998). Hence the present study had results which were lower compared to those reported by these authors because stripping was stopped as soon as blood was observed from the vent so as to avoid damaging internal organs of the brood stock. Oyelese (2006), observed that the total weight of eggs stripped from a female is dependent on the number of eggs ovulated at the time of stripping hence not a true representation of the total quantity of eggs obtained from a female spawner. However, in line with the present study, Fagade and Adebisi (1979) and  Bromage and Roberts (1995) reported that fecundity of fish is directly proportional to its body weight, therefore fecundity increased with size.

Percentage fertilization ranged from 53.5% (A x A) to 83.7% (D x C). It was observed that combinations involving the largest size (D) of female gave better fertilization compared with other combination, however the (C) Male fertilized better than (A) and (B) but comparable to the (D). Of all the combinations, crosses involving (B) females were comparable to one another irrespective of the male factor while crosses involving (C) females had one or two values comparable to other female combinations. Sperm quality of the different male brood stock might be the cause of differences in the fertilization though this was not determined in this work.

Variations in the sizes of broodstock can also lead to differences in hatching rates, as rightly observed by de Graaf et al (1995). Of all the crosses, size homogeneity did not favour fertilization and hatchability except for D x D which had the best hatchability (88.7%) with statistical differences being observed in all size combinations (P<0.05). Crosses involving (B) females gave the least hatchability compared to others. At optimum temperature of 24-30°C Abd El-Hakim (2009) observed hatching rate to increase and ranging from 48.0 to 74.3 in Common Carp, Cyprinus carpio. Oyelese (2006) also reported highest hatchability of 77.8% in C. gariepinus between 354g to 483g. Lower hatching rates have been reported for C. gariepinus by various authors. de Graaf et al (1995) reported an average rate of 59.1% in the rainy season for C. gariepinus in the Republic of Congo, while Delince et al (1987) reported a rate as low as 4% for C. gariepinus eggs incubated on a nylon substrate, which is very low compared the present study. Bartley (2002) reported that hatching success of C. gariepinus eggs is high (Mean 82.5 %) at all weights within the range of 0.1 to 1kg. Observation by Changadeya et al (2003) reveals that vendace (Coregonus albula) with low weight fish had increased hatchability than larger ones. It is however important to acknowledge that differences that arise from breeding history, age water quality and fish breed can affect hatching rates.

Conclusions

• Salami et al (1993) and Nlewadim et al (2004) reported that selection of broodstock in the African catfish has largely been through a disjointed, isolated and occasional effort unlike in the case of the American catfish (Ictalurus punctatus) and regretfully, the effect of weight to hatching rate of tropical fish eggs is poorly known. From the present study, it has been observed that an increase in the size of broodstock leads to a significant increase in fertilization and hatchability hence, there is need for further research into these crosses in earthen ponds so as to determine the true commercial application of the parental selection investigated in terms of the growth and survival of fry from different parent combinations.