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The most distinctive feature of the reproductive biology of Hoplosternum littorale is the building and guarding of an elaborate floating bubble nest. Reproduction starts at the age of one year. Males grow to a larger size than females and, during the breeding season, they develop fat deposits in the pectoral fin and an elongated recurved pectoral spine that often assumes a reddish colour. Analysis of gonadal development and surveys of nesting in swamps show that initiation of reproduction is associated with the onset of the rainy season. Males start building the nest at night, and spawning takes place around noon the day after. Most nests are built in newly flooded swamps, especially in open water in the peripheral area of the swamp. A minimum distance of 10 m between nests is usually observed. The floating bubble nest consists of a dome of plant material supported by oxygen-rich foam produced by the male. Diameter and height of the nest average 30 and 6 cm, respectively. The nest is the centre of a territory that is vigorously defended by the male, using its enlarged pectoral spine, against conspecific and heterospecific intruders. The number of nests that did not acquire spawns (48 %) suggests a strong competition among males for females. There are indications that the female drinks the sperm and that fertilization takes place after the sperm has passed through her digestive tract. Hoplosternum littorale is a multiple spawner. Investment in reproduction is high in females since they can spawn up to 14 times during a 7-month breeding season and each spawn consists of 6 000 to 9 000 eggs. On average, two to four females spawn simultaneously, resulting in an average number of 20 000 eggs per nest. Incubation of the eggs takes two to three days depending on the temperature in the nest. Despite intense predation pressure on eggs and larvae, the guarding behaviour of the male extends for only one or two days after hatching. In the hypoxic water of tropical swamps, the main function of the floating bubble nest appears to be to provide oxygen to the developing eggs by lifting the eggs above the water surface while protecting them from desiccation. Other functions of the nest may be protection of the brood against predators, temperature regulation, identification of the centre of the territory and synchronization of reproductive activities. We suggest that H. littorale may be a useful model for the study of the reproduction of tropical freshwater fish in hypoxic environments.

Sixteen batches of eggs collected immediately after spawning from five atipa (Hoplosternum littorale, (Hancock, 1828), Siluriformes, Callichthyidae) nests have been incubated at temperatures ranging from 22.5 to 32 °C. After a growing period of 8 months allowing all the fishes to express totally all secondary sexual characteristics, the sex of 9756 fishes was determined. The sexing criteria based on the color and length of the first ray of the pectoral fins are very reliable, and may lead to an error for only 0.3% of the fishes. For the 16 batches, the male sex ratio (ratio between the number of males and the total number of fishes) varies from 46.4 to 98.5% and is always greater than 50% with one exception. An overall analysis of the results shows no marked correlation (r2 = 0.312) between the proportions of males and the thermic conditions during incubation of eggs. But within each set of eggs from the same nest, this ratio systematically increases with increasing temperatures. The very low probability (0.0015) of such an event in the 15 batches of eggs from four independent nests suggests both a strong influence of the incubation temperature on the final proportion of males, and an important parental effect on the thermosensitivity of the offspring. The analysis shows clearly that a differential mortality between the sexes cannot account for the shifts towards such high proportions of males in the sex ratios. Thermosensitivity would be expressed early in this species, in the 3 days following spawning. The validity of these experimental results with regard to the natural environment as well as the potential adaptative advantage of such a mechanism for the species are discussed.

L'evolution annuelle du rapport gonado-somatique (RGS) de mâles et femelles d'atipa (Hoplosternum littorale) collectes mensuellement sur le marais de Kaw (Guyane francaise) a ete comparee au regime local des pluies. Les resultats obtenus sur les femelles ont ete compares a ceux publies pour Trinidad et Marajo (Bresil). Quel que soit le site, la valeur maximale du RGS, compris, en moyenne entre 11 et 15 selon la localite, coincide avec le premier maximum pluvieux (juillet a Trinidad, janvier a Kaw, fevrier a Marajo). Cependant, son augmentation debute pendant la saison seche (mars-avril a Trinidad, aout-septembre a Kaw, octobre-novembre a Marajo), apres une periode « refractaire » vraisemblablement obligatoire et necessaire a la reconstitution des reserves energetiques. L'analyse des donnees issues d'un echantillon plus restreint preleve sur une autre localite guyanaise (crique Macouria) confirme ce resultat. Les mesures physicochimiques de l'eau realisees sur cette derniere localite ont permis de montrer, au cours de la periode precoce de la maturation gonadique en novembre, une coincidence entre l'augmentation de la conductivite (72 a 167 μ/cm2) et celle du RGS des femelles (0 a 6 %) ou des mâles (0 a 0,2 %). Cependant, passee cette periode, bien que la valeur de la conductivite baisse (de 167 a 67 μS/cm2 de decembre a janvier), la croissance du RGS se poursuit (6 a 12 % chez les femelles; 0,2 a 0,6 % chez les mâles). La chute de la valeur de la conductivite n'enraye donc pas la poursuite du processus de maturation gonadique.

Haemonchus contortus isolates were collected from goats of five locations with different climatic characteristics in Guadeloupe archipelago. They were investigated for morphology, morphometrics and allozyme diversity after passage in immunosuppressed lambs using long acting corticoids. The basic aim of the work was to construct a synthetic strain in laboratory conditions which was representative of the isolates. The isolates were only slightly different although climatic conditions were very different. The resemblance of isolates might be due to the practice of goat exchanges between farms or to their insular origin. However the isolate from a smaller island (Les Saintes) was different (mostly on morphometrics) from all the others originating from Guadeloupe main island. The first assemblage in laboratory resulting from the installation from a mixture of the five isolates was not very representative, whereas the next generation (synthetic strain) resembled all the isolates as shown from allozyme study. Female fecundity and length in established synthetic strain were lower than that recorded in isolates, indicating a decrease in fitness, possibly due to the stability of experimental environment. The representativity of the synthetic strain was good but the strain could still evoluate on further passages and should be evaluated on a large number of generations maintained in laboratory., Des isolats d'Haemonchus contortus d'origine caprine ont été récoltés sur cinq sites de l'archipel de Guadeloupe, choisis pour leurs caractéristiques climatiques. Ils ont ensuite été maintenus chez des agneaux immunodéprimés au moyen d'un corticoïde à longue action. Des mesures morphologiques, morphométriques et d'alloenzymes ont été réalisées. L'objectif du travail était de construire, en conditions de laboratoire, une souche synthétique qui soit représentative de l'ensemble des isolats. Les isolats présentaient des différences faibles bien que les conditions climatiques soient assez variées. Ces faibles différences peuvent être imputées à l'habitude des éleveurs d'échanger des chèvres ou bien à l'origine insulaire du nématode. L'isolat issu d'une petite île (Les Saintes) était différent cependant des autres isolats de Guadeloupe, surtout par les mesures morphométriques. Le premier assemblage au laboratoire, qui résultait de l'installation des nématodes provenant des cinq isolats, n'était pas très représentatif. La génération suivante (dite souche synthétique) ressemblait toutefois à l'ensemble des isolats d'après l'analyse génétique des alloenzymes. Des différences de fécondité et de longueur des vers femelles ont cependant été enregistrées chez la souche synthétique par rapport aux isolats. Cela pourrait s'expliquer par la stabilité de l'environnement expérimental. La représentativité de la souche synthétique était donc bonne mais pourrait évoluer au cours des passages successifs; elle devrait être évaluée sur un nombre de générations plus important.

Resume Reproductive cycle and fecundity in Hoplostemum littorale (Siluriforme), reared in French Guiana. The timing of the reproductive cycle of the atipa, Hoplosternum littorale (Hancock, 1828), in ponds (batches of fishes) or in cages (isolated couples), is similar to that obsewed under natural conditions. Recordings of nests and spawning show a reproductive cycle extending from early November to the end of May. The reunion of spawners dunng the second part of the breeding season does not extend the reproductive cycle. The high density of fry in the ponds, a few months after the first spawnings, might lead to the interruption of reproduction. The breeding of isolated couples shows : a decrease in the spawn weight from the first to the third spawning to a stable value (28.5 to 23.9 g for females of average weight 89 g, and 66.7 to 21.9 g for females with average weight 207 g). The number of spawnings for a female can reach 14 over the complete reproductive cycle. The mass of eggs laid in one annual cycle by a single female, can be 180 g (48 600 eggs) for one weighing 89 g and 340 g (91 900 eggs) for one of 207 g weight. These estimations for the number of eggs, founded on the weight of an egg of 3.7 mg established in the present paper, are far beyond what had been previously mentioned. The average loss of weight of males (0.4 % of initial weight for 185 g and 9 % for 292 g males) and females (10% of initial weight for 89 g and 23 % for 207 g females) over a complete reproductive cycle shows the extent of the investment of both sexes in reproduction. In ponds, 48 % of the nests are not used for spawning. The high proportion of nests without spawn is observed during the periods preceding and following the period of maximum spawning activity (JanuaryFebmary). There is no relation between the proportion of nests without spawn and rainfall. 49% of the nests hold eggs laid by at least 2 females. Five or more females can spawn in the sarne nest. The conclusion attempts to integrate the presents results in a general view of the reproductive strategy of the atipa. It points out the need for detailed ethological studies in order to reach a better understanding of the reproductive biology of this species.

Deux series d'experiences ont ete menees, les unes en etang de pisciculture, les autres en laboratoire, pour determiner la relation entre conditions thermiques et duree de l'incubation chez l'Atipa [Hoplosternum littorale (Hancock, 1828)]. En milieu controle, 36 °C constituerait la limite superieure de la temperature d'incubation permettant la survie des œufs. La temperature minimum testee, 24 °C, ne constitue pas la limite inferieure permettant la survie des œufs. La duree minimale d'incubation, evaluee a 36 heures, serait obtenue pour une temperature d'incubation de 33,6 °C. La quantite minimum d'energie fournie par l'environnement pour obtenir l'eclosion est exprimee en degres-heures et s'eleverait a 1 201 °C × h pour la temperature d'incubation de 31,3 °C. Une typologie du developpement embryonnaire de l'espece, directement inspiree de celle de Ballantyne (1930), a ete calee sur une echelle exprimee en °C × h. En etangs, les conditions de temperature au sein de la ponte, plus elevees que celles de l'air, sont sensiblement identiques a celles de l'eau environnante et relativement stables d'une experience a l'autre (27 a 29 °C en moyenne). Le temps d'incubation observe sur l'ensemble des 9 nids equipes de capteurs varie de 47 a 54 heures. A temps d'incubation egal, le nombre de degres-heures necessaires pour obtenir l'eclosion est plus important en etang qu'en milieu controle. La discussion porte sur le role du nid dans la reproduction de l'espece.

The selection of resistant sheep in farms could increase the selective pressure during the parasitic phase and this might affect life-traits of the parasite nematodes. Before selecting for host resistance, it is crucial to estimate the potential adaptation of these nematodes to resistant hosts. The objective of this study was to determine the ability of the nematode parasite, Haemonchus contortus, to adapt its life-traits to different resistance states of sheep. The isolates of the nematode Haemonchus contortus were obtained from five locations in Guadeloupe (French West Indies) and a synthetic strain was prepared, which was representative of these isolates on the basis of isoenzymes and morphometric traits. This synthetic strain was reproduced during 10 generations in hosts of marked different resistance status. Primary infected 6-to 8-months old Black Belly ewe lambs, a wellknown to be highly resistant breed to nematode parasites, were used as resistant host. The “susceptible” lambs were obtained by treating with long-acting corticoids to depress the resistance of lambs. The establishment rate of worms and their egg-laying capacities were highly reduced in resistant lambs compared with susceptible ones. It can be assumed that the experimental design of infection apparently mimicked well the differences observed between genotypically resistant and susceptible sheep. To assess the adaptation, resistant, susceptible and naive lambs were infected with the two H. contortus lines, previously reproduced in resistant or susceptible sheep. The hosts were genetically related lambs (monozygotic twin lambs, within-litter brothers) allocated in an experimental plan designed to enhanced the power of the experiment. The use of monozygotic twins did not prove as useful as expected for parasitologi-cal data. There was no significant difference between the life-traits of the two lines. H. contortus did not seem to adapt to the resistance status of the host. Therefore, it was considered that selection for resistant sheep was possible with a limited risk of adaptation of the nematode parasites, although long-term monitoring of nematode adaptation should be scheduled if host selection is planned.