Growth performance of two African catfishes Clarias gariepinus and Heterobranchus longifilis and their hybrids in plastic aquaria

G A Ataguba, P A Annune and F G Ogbe

Department of Fisheries and Aquaculture, University of Agriculture, P.M.B 2373 Makurdi, Benue State, Nigeria
gabynotepad@yahoo.co.uk

Abstract

Hybridization of Clarias gariepinus (Cl) and Heterobranchus longifilis (Ht) and determination of their growth parameters and heterosis was carried out. Four crosses were tried (♀ × ♂): Cl X Cl, Ht X Cl, Cl X Ht and Ht X Ht. One hundred and fifty 15 day old juveniles from each of the four crosses were stocked separately in triplicate plastic aquaria. Forty fish were selected randomly every week using a fine mesh mosquito size net and then weighed in bulk on a sensitive balance.

The cross Cl X Cl had the highest final mean weight (1709mg) compared to the other three crosses. The pure breeds had similar Specific Growth Rate (SGR), 8.81%.day^-1 (Cl X Cl) and 8.82%.day^-1 (Ht X Ht). A negative heterosis for growth (-41.95%) was observed in the hybrids while survival of the hybrids showed a positive heterosis (29.4%). Poor growth of hybrids accounted for the negative heterosis. Hence crossbreeds survived better than the pure breed catfishes. There was no significant difference in specific growth rate among the four genetic groups studied (P>0.05).

Key words: Heterosis, hybridization, survival rate, weight gain

Introduction

Aquaculture production of the African catfishes Clarias gariepinus and Heterobranchus longifilis has been practiced for a long time in Africa. Increased productivity of fry and fingerlings with attributes of faster growth rates and better environmental tolerance is sine qua non to ensuring fish food security in Africa. Genetic techniques are therefore needed to ensure that a faster growth rate leading to a shorter production cycle as well as a greater tolerance for poor water condition is achieved. The USDA (1988) pointed out that the lack of reliable estimates of genetic parameters such as genetic and phenotypic variances, covariance, and genetic and phenotypic correlations for commercially important traits and the lack of designed selection programs to test their validity as the major constraints to rapid development of stocks for commercial production of aquaculture species.

Hybridization between some species of tilapias such as Oreochromis niloticus x Oreochromis aureus results in the production of predominantly male offspring and reduces unwanted natural reproduction in grow-out ponds (Rosenstein and Hulata 1993). Legendre et al (1992) investigated hybridization of the two African catfishes: Clarias gariepinus and Heterobranchus longifilis. These authors reported viability in reciprocal hybrids with their survival rates being similar to those found in the maternal species. Furthermore, Sahoo et al (2003) investigated hybridization between two clariids: Clarias batrachus (Linn.) x Clarias gariepinus (Bur.) and performance of the offspring in rearing operations. Nwadukwe (1995a) reported the growth performance of Clarias gariepinus and Heterobranchus longifilis and their F₁ hybrids with the reciprocal cross showing intermediate growth rate between both parents. Aluko (1995) reported that crosses between male Heterobranchus longifilis and female Clarias anguillaris were significantly heavier and longer than the reciprocal cross. Nwadukwe (1995b) reported similar mean weights for backcross F₁ progeny of Clarias gariepinus and Heterobranchus longifilis. This study was designed to test the crossbreeds of the two genera for growth and survival heterosis.

Materials and methods 

The broodstocks of Clarias gariepinus and Heterobranchus longifilis of known breeding records were obtained from the University of Agriculture Makurdi Teaching and Research Farm. Crosses of these species and their reciprocal crosses were carried out in the hatchery. These were labeled as: Cl X Cl (Clarias gariepinus X Clarias gariepinus), Ht X Ht (Heterobranchus longifilis X Heterobranchus longifilis), Ht X Cl (Heterobranchus longifilis X Clarias gariepinus) and Cl X Ht (Clarias gariepinus X Heterobranchus longifilis). In all the crosses the female is mentioned first (♀ × ♂). Oocyte diameter of females was measured using a micrometer screw gauge with a sample size of forty oocytes. Females with oocyte diameters of 1.3 – 1.5 mm were selected and kept in tanks. Oocyte maturation and ovulation was induced by a single intramuscular injection of Ovaprim (an analog of salmon gonadotropin releasing hormone (sGnRHa) and a dopamine inhibitor)  at a dose of 0.5 ml kg^-1. Time between injection and ovulation was 12 hours and 15 hours for Clarias gariepinus and Heterobranchus longifilis respectively. After ovulation, eggs were collected by manually pressing the abdomen in the direction of the caudal fin into a dry clean plastic bowl. Milt was obtained via surgical removal of the testes. Sperm was extended in 0.9% NaCl solution. Ova were fertilized by adding the extended milt mixture. The resulting mixture was stirred using a feather for one minute to ensure complete fertilization then triplicate batches of eggs from each cross were incubated in 60L plastic aquaria with flow through water system using rubber type mosquito mesh netting as substrate. Three females and two males were used for each cross. A control sample of eggs that were 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.

Hatchlings were transferred to concrete tanks of 2.4m X 1.2m X 1.0m to be reared for 15 days. They were fed ad libitum twice daily with dried decapsulated cysts of Artemia sp. After one week of feeding, the fish were introduced gradually to an artificial dry diet of coppens (200 – 300 µm) catfish feed. Artemia and the artificial dry diet were offered alternately to the larvae during the weaning period which lasted four days.

One hundred and fifty 15 day old juveniles from each of the four crosses Cl × Cl, Ht × Ht, Ht × Cl, and Cl × Ht were stocked separately in triplicate 60L plastic aquaria with water continuously aerated and renewed totally every three days. Fish were fed ad libitum two times a day with coppens catfish feed beginning with 200 – 300μm followed by 2mm after five weeks. The experiment lasted for fifty six days and mean fish weight in each tank was determined every week beginning from the day they were stocked in the tanks. Waste removal was done via siphoning every three days. For sampling, 40 fish were selected randomly using a fine mesh mosquito size net and then weighed in bulk on a sensitive balance. After the 56 days period, the surviving juveniles were counted and all fish from the tank were weighed in bulk.

Parameters determined include:

Where: W₀ = initial mean body weight,

W₁ = final mean body weight and t = time in days.

The mean weights and surviving number of the crossbreeds and the pure breeds were used to ascertain heterosis for growth and survival, respectively. Heterosis here refers to the performance whether growth or survival of the crossbreeds relative to that of the purebreds as expressed in percentage by the formula (after Nguenga et al 2000):

Where C₁ and C₂ are the mean weight or survival of crossbreeds, and P₁ and P₂ are the mean weight or survival of the purebreds.

Growth and survival rates were compared using one-way analysis of variance (ANOVA) and Fisher’s LSD to determine significant differences between means. Since mean initial weights differed significantly among the genetic groups studied, the specific growth rate (SGR) of the fish were compared using Analysis of covariance with the initial weight serving as covariate.

Results 

Table 1 shows the mean initial weight, mean final weight, weight gain, growth rate (GR), specific growth rate (SGR) and survival rate (SR) for pure breeds and crossbreeds of two African catfishes Clarias gariepinus  and Heterobranchus longifilis reared under hatchery conditions in plastic aquaria for 56 days.

The pure breeds showed lower survival rates (37.8% and 38.7% for Cl X Cl and Ht X Ht respectively) than the inter-generic hybrids. The survival rate for the cross Ht♀ X Cl♂ was significantly different from the other crosses (P<0.05). The growth rates of the two hybrids: Ht♀ X Cl♂ and Cl♀ X Ht♂ were significantly lower than those of the pure breeds. In terms of final mean weights, the cross Cl X Cl had a significantly (P<0.05) higher weight (1710mg) than the other three crosses . The pure breeds have a close SGR, 8.81%.day^-1 and 8.82%.day^-1 for Cl X Cl and Ht X Ht respectively. These were however not significantly different from those of the hybrids (P>0.05) with values of 7.85%.day^-1 and 7.97%.day^-1 for Ht♀ X Cl♂ and Cl♀ X Ht♂, respectively.

Table 2 shows heterosis for the various stages of development of progeny of the crosses.

The hybrids displayed a negative heterosis for growth (-42%) due to their poor growth compared to the pure breeds after 56 days period. In terms of survival, the hybrids showed a positive heterosis (29.4%) after 56 days of rearing. Growth pattern is similar for all the crosses (Figure 1).

Discussion 

The survival rate of the cross Ht♀ X Cl♂ differed significantly from the other crosses (P<0.05). Values obtained for survival rates are comparable to those obtained for the same combination of crosses as reported by Nlewadim et al (2004) except for the cross Cl♀ X Ht♂ which they reported had a survival rate of 87%. Also, de Graaf et al (1995) reported a survival rate of 41.5% for Clarias gariepinus reared under a medium stocking density for a short duration in protected tanks.

The final mean weights of the four genetic groups under study ranged from 684 mg to 1710mg. The cross Cl♀ X Ht♂ showed the least final mean weight gain with 684mg. This is significantly lower than the values of 2250mg reported for the same cross by Nlewadim et al (2004). However, the final mean weight value of 1710mg as recorded for Cl X Cl is comparable to the value of 1950mg as reported by Nlewadim et al (2004). The weight gain of these genetic groups also follow the same pattern as the final mean weights. The final mean weight of the cross Cl X Cl differed significantly from the other three genetic groups (P<0.05, F-LSD). In terms of weight gain, there was no significant difference (P>0.05) in values obtained for Cl X Cl and Ht X Ht and these differed significantly from those for the other two crosses Ht♀ X Cl♂ and Cl♀ X Ht♂ which were also not significantly different from each other (P>0.05). The weight gain of 1069mg obtained for the cross Ht X Ht is significantly lower than those obtained for crosses of two strains of Heterobranchus longifilis as reported by Nguenga et al (2000).

There was no significant difference in specific growth rate among the four genetic groups studied (P>0.05). de Graaf et al (1995) reported a specific growth rate of 6.9%.day^-1 for Clarias gariepinus stocked at a low stocking rate and reared for a long period (≥51 days). This is lower than the value of 8.81%.day^-1 discovered in the present study. The SGR of 8.82%.day^-1 reported in the present study  for the cross Ht X Ht is significantly higher than the range of 2.12%.day^-1 to 3.96%.day^-1 as reported for various strains of Heterobranchus longifilis  by Nguenga et al (2000). Nlewadim et al (2004) reported SGR of 12.0%.day^-1, 11.6%.day^-1, 11.2%.day^-1 and 11.0%.day^-1 for the crosses: Cl X Cl, Ht X Ht, Ht♀ X Cl♂ and Cl♀ X Ht♂, respectively. These are however higher than the values of 8.81%.day^-1, 8.82%.day^-1, 7.85%.day^-1 and 7.97%.day^-1 reported in the present study for the crosses: Cl X Cl, Ht X Ht, Ht♀ X Cl♂ and Cl♀ X Ht♂, respectively. The pure breeds had a very close SGR with Ht X Ht having the highest (8.82%.day^-1) followed by Cl X Cl (8.81%.day^-1). The least SGR (7.85%.day^-1) was recorded for the cross Ht♀ X Cl♂.

The crossbreeds showed a negative heterosis for growth (–42). This is as a result of their poor growth but they displayed a positive heterosis for survival (29.4) after 56 days of rearing. The negative heterosis value for growth shows that a negative interaction has occurred between the parental genes found at different loci in the inter-generic hybrid genome as reported by Sheridan (1981).  The phenotypic variance of a quantitative trait such as growth and survival is governed by the genetic variance, environmental variance and the interaction between the genetic and environmental variance (Tave 1993). A negative interaction between the genetic variance of the hybrid and the environment may have led to poor phenotypic expression of growth.

Nguenga et al (2000) reported a net positive heterosis of 89.5% for crosses between two strains of Heterobranchus longifilis. Cross breeding of Clarias spp. and Heterobranchus longifilis has been carried out by various authors (Aguigwo 1993; Aluko 1995; Nwadukwe 1995a; Nlewadim et al 2004; Odedeyi 2007) but heterosis for growth or survival of the resulting hybrids was not calculated.

Conclusions

• There is need for further research into these crosses in earthen ponds so as to determine the true commercial application of the inter-generic crosses investigated here. This is important since the crossbreeds displayed a positive heterosis for survival hence greater numbers of fry and fingerlings surviving to adult stage. Further research will also focus on the manipulation of growth using different levels of protein since specific growth rates did not differ among the four genetic groups studied.

References 

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Received 29 November 2009; Accepted 5 January 2010; Published 7 February 2010

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