A comparison of the aquaculture potential of Clarias gariepinus (Burchell, 1822) and its hybrid with Heterobranchus longifilis valenciennes, 1840 in Southern Africa
- Authors: Oellermann, Lawrence Keith
- Date: 1996
- Subjects: Aquaculture -- South Africa Clarias Clariidae Catfishes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5246 , http://hdl.handle.net/10962/d1005089
- Description: The aim of this study was to evaluate the aquaculture potential of a hybrid between the two largest African silurid catfish, Heterobranchus longifilis (HL) and Clarias gariepinus (CG) . A morphometric, meristic and karyological study showed that the hybrid shared some of the physical characteristics of both C. gariepinus and H. longifilis, while its chromosome complement and fundamental number (2N = 54, FN = 95), was intermediate between that of H. longifilis (2N = 52, FN = 92) and C. gariepinus (2N = 56, FN = 97). The HLxCG cross could therefore be regarded as a true hybrid. For the characters tested, no morphological or karyological differences were apparent between the HLxCG hybrids produced in West Africa and those produced in southern Africa. In southern Africa, the HL♂xCG♀ cross had higher fertilization and hatching rates than pure strain H. longifilis, C. gariepinus or the reverse cross. There was no difference in the survival of the HL♂xCG♀ hybrid larvae and C. gariepinus larvae up to the onset of exogenous feeding. Pure strain H. longifilis juveniles had a faster growth rate than the H. longifilis ♂ x C. gariepinus ♀ juveniles, but the hybrid always grew at a faster rate than C. gariepinus or the reverse cross. The HL♂xCG♀ cross was consequently chosen as the hybrid with the greatest potential for siluroid aquaculture in southern Africa. The HL♂xCG♀ hybrid showed evidence of partial gonadic, gametic and post-zygotic sterility in both sexes. The hybrid was not completely sterile, as it was artificially induced to spawn, and a small number of viable F₂ hybrid and F₁ hybrid x C. gariepinus larvae were produced. However, in the light of its probable reproductive strategy, it is highly unlikely that the hybrid would pose an ecological risk to the southern African region. The H. longifilis ♂ x C. gariepinus ♀ hybrid was compared to C. gariepinus for selected water quality preferences and tolerances. The hybrid had a wider temperature preference (28 °C to 34 °C) than C. gariepinus (28 °C to 30 °C), but appeared to be more dependent on aerial respiration than C. gariepinus. The air-breathing frequency of hybrid fish began to increase at dissolved oxygen concentrations below 3 .8 mg.ℓ⁻¹, while C. gariepinus only showed an increase in air-breathing frequency at concentrations below 3.0 mg.ℓ¹. The hybrid was more tolerant of un-ionised ammonia (96-hour LC₅₀ = 9.1 mg.ℓ⁻¹) than C. gariepinus (96-hour LC₅₀ = 6.5 mg.ℓ⁻¹), but their 96-hour LC₅₀ salinity tolerances were similar (10.8-11.0 g.ℓ⁻¹). The H. longifilis ♂ x C. gariepinus ♀ hybrid had a higher fillet yield (43.9 %) than C. gariepinus (38.9 %), but the crude protein content and amino acid profile of the two groups were similar. Catfish are traditionally grown in earthen ponds under semi-intensive conditions in southern Africa, at around 4 kg of fish per cubic meter of water (kg.m⁻³). However, the hybrid could tolerate densities of up to 415 kg of fish per cubic metre of water, if the water was exchanged hourly (kg.m⁻³.hr⁻¹), and the density at which yield was optimised was rounded off to 400 kg.m³.hr⁻¹. The high threshold density and water quality tolerances of the H. longifilis ♂ x C. gariepinus ♀ hybrid indicates that it is ideally suited for highly intensive aquaculture. It was concluded that it would be more productive to farm the HL♂xCG♀ hybrid on an intensive basis in southern Africa, than it would be to farm C. gariepinus in the traditional manner.
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- Date Issued: 1996
The karyology and taxonomy of the southern African yellowfish (Pisces : cyprinidae)
- Authors: Oellermann, Lawrence Keith
- Date: 1989
- Subjects: Barbus -- South Africa Cyprinidae -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5192 , http://hdl.handle.net/10962/d1001968
- Description: The southern African yellowfish (Barbus aeneus, B. capensls, B. kimberleyensis, B. natalensis and B. polylepis) are very similar, which limits the utility of traditional taxonomic methods. For this reason yellowfish similarities were explored using multivariate analysis and karyology. Meristic, morphometric and Truss (body shape) data were examined using multiple discriminant, principal component and cluster analyses. The morphological study disclosed that although the species were very similar two distinct groups occurred; B. aeneus-B. kimberleyensis and B. capensis-B. polylepis-B. natalensis. Karyology showed that the yellowfish were hexaploid, B. aeneus and B. kimberleyensis having 148 chromosomes while the other three species had 150 chromosomes. Because the karyotypes of the species were variable the fundamental number for each species was taken as the median value for ten spreads. Median fundamental numbers were B. aeneus = 196, B. natalensis = 200, B. kimberleyensis = 204, B. polylepis = 206 and B. capensis = 208. The lower chromosome number and higher fundamental number was considered the more apomorphic state for these species. Silver-staining of nucleoli showed that the yellowfish are probably undergoing the process of diploidization. Southern African Barbus and closely related species used for outgroup comparisons showed three levels of ploidy. The diploid species karyotyped were B.anoplus (2N=48), B. argenteus (2N=52), B. trimaculatus (2N=42-48), Labeo capensis (2N=48) and L. umbratus (2N=48); the tetraploid species were B. serra (2N=102), B. trevelyani (2N=±96), Pseudobarbus afer (2N=96) and P. burgi (2N=96); and the hexaploid species were B. marequensis (2N=130-150) and Varicorhinus nelspruitensis (2N=130-148). The taxonomic implications of polyploidy for the African cyprinids were considered, and its effect on species was discussed.
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- Date Issued: 1989