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First results on the diversity of monogenetic parasites from catfishes in South-East Asia are presented. Fifty-five different species belonging to two already known and one new genera were found among which 3 or 4 were previously described. The general host parasitic species richness and parasitic specificity are summarized. Implications of these two descriptors at host species and population levels are discussed. (Résumé d'auteur)

Fish unlike terrestrial animals, use a large amount of protein as an energy source for their energy metabolism. When fed on a high protein raiton, the fish itself may choose which amount of protein in food will be converted into body growth and which will be burned through the catabolism. Therefore, in the study one diet was designed with a high protein content and fed to fish with different levels : 0, 5, 15, 25, 35 and 45 g crude protein kg/d. #P. bocourti$ has a higher growth rate than #P. hypophthalmus$ at the same food intake. However, the higher growth observed in #P. bocourti$ is obviously associated to higher fat accumulation in the body. The protein efficiency, NPU and PER, tends to be reduced at higher protein intake in both species. Energy and protein requirements for maintenance were calculated to be 128 and 92 kJ/kg/day, and 5.16 and 3.24 g/kg/day, and #P. bocourti$ and #P. hypophthalmus$, respectively. #P. bocourti$ has nearly a double protein and energy requirement for maintenance. The event may be linked to the fact that #P. bocourti$ has a higher growth rate and higher ability to synthesise a large amount of body lipid than #P. hypophthalmus. An estimate of protein requirement was in the range of 12-13 and 11-12 g/kg/day in #P. bocourti$ and #P. hypophthalmus$, respectively. The DP/DE ratio was estimated to be 18 and 17 mg/kJ in #P. bocourti$ and #P. hypophthalmus$, respectively. These low DP/DE ratios may be related to the fact that the protein requirement was relatively low in the two species. (Résumé d'auteur)

Catfishes, 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)

Two 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)

Observations on growth rate and occurrence of first sexual maturity were done on a population of 75 #Pangasius djambal$ originally caught in the wild, individually tagged, and reared in 200 m2 ponds at a stocking density of 0.4-0.5 fish/m2 at the Sukamandi research centre (Java). These fish, weighing initially between 190 and 1100 g were fed with a 35-40% crude protein pelleted feed and followed up during a period of 16 months. Two trials of induced ovulation were also carried out on females from a small stock of a dozen adult fish reared in floating cages at the Danau Teluk fish culture station (Sumatra). Between June 1997 and October 1998, the mean body weight of fish increased from 555 g to 4162 g, which corresponded to a daily weight gain of 7.4/d. The highest individual growth rate observed between two successive sampling dates was of 16.5 g/d. The mean growth rate of #P. djambal$ females (8.9 plus or minus 2.2 g/d) was significantly higher than that of males (6.3 plus or minus 1.9 g/d) and first sexual maturity occurred several months earlier in males than in females. Oocyte maturation and ovulation were induced with two successive injections of Ovaprim at 8 h interval, corresponding to a total dose of 0.9 mL/kg. Among four females treated, three ovulated and could be stripped. Mean hatching rates obtained after artificial fertilisation of eggs varied between 8 and 31%. After 27 days of age, the survival rate of larvae fed live #Artemia$ nauplii then dried feed was 61%. No cannibalism was observed during the larval rearing which did not appear as a critical phase of the breeding cycle. Although preliminary, these results confirm the great potential interest of using #P. djambal$ for aquaculture. The induced breeding and larval rearing carried out for the first time in this species represent a breakthrough in the control of its biological cycle in captivity. (Résumé d'auteur)

Fourteen dinucleotide DNA microsatellite loci were screened in the catfishes #Clarias gariepinus$, #C. batrachus$ and #Pangasius hypophthalmus$. They will be used for the screening of wild and cultured populations. (Résumé d'auteur)

A 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)

Over a 2-year period at the Sukamandi station (West Java, Indonesia), 87 #P. hypophthalmus$ females selected on the basis of a modal oocyte diameter greater than 1.0 mm were treated with Ovaprim (n=77) or hCG (n=10) to induce oocyte maturation and ovulation. The two hormonal treatment led to similar results in terms of ovulation percentage (86 and 90%), hatching rates (69 plus or minus 28 and 82 plus or minus 11%) and relative fecundity (167,000 plus or minus 18,000 and 128,000 plus or minus 60,000 eggs/kg, with Ovaprim and hCG respectively. The latency period between the last hormone injection and ovulation was negatively correlated to water temperature but showed important variations at a same temperature depending on individual females (e.g. between 5-11 h at 28-29°C). The ovulation time was therefore difficult to predict accurately in this species. The assessment of survival time of ova maintained in ovario after ovulation showed that the process of ageing (overripening of ova) occurs rapidly in #P. hypophthalmus$. The overall quality of ova begun to decrease as early as 2 hours after ovulation and, after 3 hours, hatching rate dropped down and fraction of deformed larvae increased significantly in comparison to those observed at the moment of ovulation. In some individual females this evolution was even more rapid, with a sharp decrease in hatching rates between 1 and 2 hours post-ovulation. The duration of ova survival did not appear to depend on the type of hormonal treatment used (Ovaprim or hCG). For optimised gamete management in hatcheries, it is therefore recommended to check carefully the females for the occurrence of ovulation (between 3 to 11 h after the last hormone injection, depending on water temperature) and to collect and fertilise the eggs within less than two hours after this moment. (Résumé d'auteur)

With 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)

RFLP analysis of mitochondrial DNA (mtDNA) was used to study variation within 13 populations of #Clarias batrachus$, sampled respectively in Vietnam, Thailand and in the Indonesian Archipelago. In this study an amplified region corresponding approximately to 2.3 kilobases of the Cytochrome-b and D-loop genes was digested using 8 restriction enzymes (HinfI, Hin6I, MvaI, MspI, HaeIII, BanHI, NdeII, DraI). 12 mtDNA haplotypes were found in 40 specimens. Each sampling location was characterised by one haplotype, except Palembang (Sumatra, Indonesia) and Samarinda (Kalimantan, Indonesia) where 2 and 4 haplotypes were found respectively. The consensus tree calculated from 15 more parsimonious networks showed that mtDNA haplotypes are geographically distributed. Three well differentiated clusters were identified. The first cluster is composed by populations from both Thailand and Vietnam, the second cluster by two populations from West Sumatra between populations which come from highlands (altiude more than 1000 meters in Bukittingui, and 300 meters in Nias Island) and populations located in lowlands. The significant genetic relatedness observed between populations from Sumatra (Jambi, Palembang, Muara Tebo, Teluk Kuantan) and populations from Java indicate a possible common origin which is probably in Kalimantan. This result is supported by the high diversity of haplotypes revealed in Samarinda (Kalimantan) and their intermediate position in the genetic network. The populations from highlands in West Sumatra which share a common haplotype are genetically more related to populations from Thailand and Vietnam than to populations from the rest of Indonesia. These populations seems to be relict populations from a first colonisation event which arise from the continental part of Asia... (D'après résumé d'auteur)

As 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)

An 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)

One of the main problems that has to be faced by #Pangasius hypophthalmus$ breeders is the high mortality of the larvae, which can be a consequence of both cannibalism and bacterial diseases. The aim of this study was to explore the possible sources of #Aeromonas hydrophila$ that may result in an infection of #Pangasius hypophthalmus$ larvae. Isolation of bacteria was made from water source, #Artemia$ culture medium, #Artemia$ nauplii used as feed, ova (unfertilised eggs), sperm, and fed as well as unfed larvae that were collected every day from hatching, up to the age of 7 days. Characterisation of bacteria was done on the basis of morphological, physical and biochemical characteristics. The serological method of identification using polyclonal #Aeromonas hydrophila$ antiserum was used. The results indicated an absence of bacteria from sperm. By contrast, bacteria #Alcaligenes$ sp. were isolated from source of water, unfertilised eggs and from 1-day-old larvae. #Proteus$ sp. were isolated from the 1st day of age in fed larvae and from the 7th day in unfed larvae. #Aeromonas hydrophila$ were isolated from larvae of 2 days of age, and #Aeromonas punctata$ from 2-days-old unfed larvae, meanwhile #Plesiomonas shigelloides$ were identified from fed larvae of 2 and 4 days of age, and from 2-days-old unfed larvae. (Résumé d'auteur)

Ten crosses between five #Clarias$ species of African (#C. gariepinus$) and Asian origin (#C. batrachus$, #C. meladerma$, #C. nieuhofii$ and #C. teijsmanni$) were evaluated on the basis of the fertilisation and hatching rates obtained. Zootechnical performances (growth, survival) of #C. batrachus$ and #C. gariepinus$ larvae were compared. Viable hybrids growth and survival were followed up until the age of 11 weeks. The genotype of the reciprocal crosses between #C. gariepinus$ and #C. meladerma$ was studied and the gonad development of two-years-old #C. meladerma$ x #C. gariepinus$ hybrids were examined (inter-specific crosses are always given with the female parent in the first position). No hybrid between #C. gariepinus$ and #C. batrachus$ could be obtained. #Clarias gariepinus$ x #C. nieuhofii$ and #C. gariepinus$ x #C. teijsmanni$ hybrids did not survive more than a few hours after hatching and larvae obtained from #C. gariepinus$ x #C. meladerma$ cross were non viable beyond a few days afer hatching. In the latter case, protein electrophoresis of progeny carried out at two loci diagnostic for #C. gariepinus$ and #C. meladerma$) (PGI and PGM) indicated that the larvae resulted from an haploid gynogenetic development. The crosses between female #C. meladerma$ and male #C. gariepinus$ or #C. nieuhoffi$ or #C. teijsmanni$ produced viable hybrids. #Clarias gariepinus$ and #C. batrachus$ zootechnical performances comparison during larval rearing indicated that the growth potential of these two species is equivalent until the age of 12 days, though #C. gariepinus$ is favoured by its larvae bigger initial size. The comparison of #C. gariepinus$ and #C. meladerma$ x #C. gariepinus$ growth and survival until the age of 11 weeks showed good performances in the hybrid compared to the Asian species but slightly lower than the ones observed in #C. gariepinus... (D'après résumé d'auteur)