1,721,168 research outputs found
The biological diversity and aquaculture of clariid and pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textCatfishes, and in particular #Clariidae and #Pangasiidae, are important aquatic resources in Asia, where their culture represented an annual production of about 124,000 t in 1993. In the clariids, this production results mostly from the use of F1 hybrids between the introduced African catfish (#Claris gariepinus) and various local clariid species. In the pangasiids, various culturing techniques were empirically developed for some native species, whose juveniles are most often captured in the wild. Further development of this catfish culture industry faces serious problems related to the poorly known systematic of these fish groups, the scarce knowledge of the biology and aquaculture potential of autochthonous species, the limitation of seed supply and the declining performances reported in some cultivated stocks. In this context, the "Catfish Asia" project which deals with the two catfish families, #Clariidae and #Pangasiidae$, has the main following goals : to acquire a stronger knowledge of the biological diversity of SE Asian catfishes and to enhance its utilisation through a correct identification and characterisation of valuable species, populations and strains of aquaculture interest. This approach represents an important precondition to the sustainable management of cultivated and natural stocks and to guide conservation efforts of these economically important resources. It will also contribute to a better knowledge of their phylogeographic relationships ; to acquire sound biological bases for the development of catfish culture in the SE Asian region. The evaluation of the aquaculture potential of the autochthonous species (diversification) and the optimisation of their rearing cycle (artificial propagation) through technologies adapted to the local conditions are essential elements for a better production in the future... (D'après résumé d'auteur
The biological diversity and aquaculture of clariid and pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textWith the aim of detecting phylogenetic relationships among #Pangasiidae catfishes, 23 enzyme loci were studied on 18 nominal species of the genera #Pangasius and #Helicophagus (Roberts and Vidthayanon, 1991). In order to assess the taxonomic position of #Laides genus in the #Schilbeidae or in the #Pangasiidae, 2 species belonging to the genus #Laides and 1 species of the genus #Pseudeutropius (#Siluriformes, #Schilbeidae) were added in the study. The results indicate that the species #Laides hexanema and #Laides sinensis appear to be genetically related with the #Pangasiidae. The phylogenetic tree obtained shows a clustering of species which validate the genus #Helicophagus but indicates that the genus #Pangasius is polyphyletic. The genus #Pangasius is composed of 3 genetic differentiated groups. Group 1 is composed of 3 species belonging to two different morphological entities validated by Roberts and Vidthayanon (1991) as possible subgenus. #Pangasius hypophthalmus and #P. gigas which share common genetic characters validate the subenus #Pangasianodon. The possession of many private alleles by #P. pleurotaenia confirms the morphological originality of this species which was therefore considered to belong to the monotypic subgenus #Pteropangasius. The second groupd consists of #P. micronema, #P. macronema, #P. lithostoma and #P. polyuranodon and the last group represents all the other species of the genus #Pangasius. By contrast #Neopangasius considered as a possible subgenus by Roberts and Bidthayanon (1991) is polyphyletic. Although relative genetic similarities were found between #P. humeralis and #P. nieuwenhuisii which are located in group 3, the species #P. lithostoma appears to be more closely related to species belonging to the group 2... (D'après résumé d'auteur
The biological diversity and aquaculture of clariid and Pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textAn evaluation of the seasonal variations of sexual activity of #P. hypophthalmus broodstock held in 50 m2 ponds was carried out between April 1997 and April 1998 at the Sukamandi station (West Java, 6°S of latitude). These variations were assessed through the evolution of oocyte diameter of individual females, the proportion of fluent males and the success of hormonal-induced breeding trials. High proportions of fluent males and mature females with post-vitellogenic oocytes of modal diameter superior to 1.00 mm were found at anytime. As a consequence, successful induced breeding of this species using hormonal treatments could be performed regardless of season and allowed an all year long production of fry. This continuous sexual maturity of #P. hypophthalmus broodstock, during both the dry and rainy seasons, may have resulted to a large extent from rather stable conditions, with a monthly mean water temperature constantly high (28-31°C) and a low variation of day length during the year. Ovulation was successfully induced at 3, 2 and 4 months interval in a same #P. hypophthalmus$ female. This indicated a quick recovery of oogenesis in females reared in the ponds. (Résumé d'auteur
The biological diversity and aquaculture of Clariid and Pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textA morphometric analysis of wild and cultured #Clarias specimens originating from Vietnam indicated the presence of three species : #C. batrachus, #C. macrocephalus and #C. gariepinus. The latter is an African species that has been introduced for fish culture purposes. The status of a fourth species, #C. fuscus$, previously reported from the northern part of the country, could not be clarified yet as no material could be examined. This is the subject of forthcoming research. (Résumé d'auteur
The biological diversity and aquaculture of clariid and pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textAs part of an ongoing systematic revision of the South-East Asian #Clarias species, this paper presents the results of a morphometric study of 317 specimens from Indonesia : 255 of them who collected from the wild in Sumatra and Kalimantan and 62 came from fish culture stations in Java and Sumatra. The results obtained indicated the presence of five or six species : #Clarias batrachus, #C. macrocephalus (?), #C. meladerma, #C.leiacanthus, #C. teijsmanni and #C. nieuhofii$. Preliminary identification characters are given. (Résumé d'auteur
The biological diversity and aquaculture of clariid and pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textThe influence of an incubation system on embryo development and subsequent survival of larvae was evaluated on eggs from two #P. hypophthalmus$ females. All tests were performed at a same temperature of 28.5-29°C, given by the water of a re-circulating system to which all incubation devices were connected. The following situations were tested : 1) Happa (adhesive eggs) ; 2) floating screen net (adhesive eggs) ; 3) McDonald type incubator (stickiness of eggs being suppressed with a clay suspension) ; 4) plastic basket with water from the re-circulating system (stickiness of eggs being suppressed with a clay suspension) ; 5) plastic basket with water from the re-circulating system (adhesive eggs) ; 6) plastic basket with mineral water (adhesive eggs). No significant difference was found in hatching rates whatever the conditions of egg incubation. The development time and hatching kinetic were very similar in all systems ; at 28.5-29.5°C, the first hatched larvae were observed between 19 and 21h post-fertilisation and the duration of the hatching period lasted 6 to 8 h. However, hatching tended to occur slightly earlier in the McDonald type incubator, probably as a consequence of mechanical agitation of eggs. Up to the age of 4 days, no significant difference was found in the survival of larvae as a function of the type of incubator from which they were issued. All together, the results indicate that, when properly managed, the incubation methods can hardly be responsible for the variability of hatching rates or survival of larvae often observed in different reproduction trials or from farm to farm. (Résumé d'auteur
The biological diversity and aquaculture of clariid and pangasiid catfishes in South-East Asia : proceedings of the mid-term workshop of the "Catfish Asia project"
No full textTwo feeding experiments were carried out on #Pangasius hypophthalmus larvae reared in a recirculating water system during 8 days. The first experiment was done at the Can Tho University (Vietnam) and the second at the RIFF Sukamandi station (Indonesia). The main objective of the first experiment was to compare survival and growth peformance of #P. hypophthalmus larvae fed with either #Moina sp. or #Artemia nauplii and with either strong or moderate aeration. Strong aeration was tested in order to homogenise prey repartition in the water column, since #Artemia and #Moina sp. tended normally to be concentrated in corners or at the bottom of the tanks. Two feeding rates (150 and 4000% of fish biomass) were tested. The second experiment aimed at an evaluation of optimal feeding level with #Artemia nauplii, by considering growth, number of ingested preys and survival rates of larvae. Each of three feeding levels (R1, R2 and R3) were tesed at three different fish stocking densities (10, 30 and 90 larvae/L). The feeding level R1 was adjusted daily according to a pre-established model of the number of #Artemia ingested as a function of age in #P. hypophthalmus larvae. The rations R2 and R3 were respectively 3 and 9 times greater than R1. The prey asscessibility (number of prey per litre), which varied as a function of the different combinations of feeding level x fixh stocking density, was also considered as a parameter that could influence larval growth and survival. The results of the first experiment indicated that both #Artemia and #Moina sp. could be used as a first feed for #P. hypophthalmus larvae. However, larvae fed #Artemia nauplii presented a faster growth rate than those fed #Moina. Perturbation of the rearing media by strong water aeration resulted systematically in reduced larval survival rates, whatever the type of prey and feeding rate used... (D'après résumé d'auteur
The third international symposium on tilapia in aquaculture
No full textThe year-round, spontaneous and continued reproduction of tilapia in captivity was initially regarded as an unexpected asset for African aquaculture development, but it was quickly found to be a serious handicap when farming the fish in ponds due to the resulting population. Various techniques have overcome this obstacle. The reproductive efficiency of tilapia has advantages and disadvantages for the supply of fry to fish farmers. Among the advantages is the possibility for fish farmers to produce their own fry ; among the disadvantages is the difficulty to control the broodstock quality. The low number of eggs in each spawning requires the use of a large number of broodstock and the asynchrony of spawnings makes the simultaneous production of large quantities of graded fry difficult. Finally, the control of undesirable reproduction in farming involves the use of monosex populations. These issues are analyzed and discussed in relation to development strategies, microeconomics and the identification of research themes that can be developed to improve the different options. The data for three species of tilapia (#Oreochromis niloticus, #Sarotherodon melanotheron and #Tilapia guineensis) are compared to the data for two species of African catfish of the family #Clariidae (#Claris gariepinus and #Heterobranchus longifilis) that require induced reproduction techniques, but are far more fertile. (Résumé d'auteur
- …
