Arapaima gigas is an air-breathing giant fish of Amazonian rivers. Given its great economic and cultural importance, the aquaculture development of this species represents an evident solution to face the decline of wild populations. In captivity, reproduction occurs generally in large earthen ponds where stocks of a few tens of brooders are maintained together at the beginning of the rainy season (December-March in the Peruvian Amazon). Fry production relies on the spontaneous formation of male and female pairs, which build a nest, delimit a territory and guard the offspring for at least 20 days from other congeners and predators. However, as sex determination of A. gigas is not possible by morphological criteria, it is very difficult to optimize reproduction conditions and fry production in each pond, which seriously hampers the culture of this species. This situation prompted us to develop sexing methodologies based on (1) the detection of female specific plasma Vitellogenin (Vtg) using an enzyme immuno assay (EIA), and (2) the determination of plasma 17beta-estradiol and 11-ketotestosterone levels for immature specimens. The Vtg purification was performed by electro-elution after polyacrilamide gel electrophoresis (PAGE) from plasma of 17beta-estradiol treated A. gigas juveniles. Two different Vtg molecules were isolated, (Vtg(1) and Vtg(2)) with 184 and 112 kDa apparent molecular masses, respectively, and two antibodies were raised in rabbits for each Vtg molecule. Adult fish were 100% accurately sexed by Vtg EIA, while 100% of immature fish and 95% of adults were accurately sexed by 17beta-Estradiol and 11-Ketestosterone ratios. We also observed different color pattern development in male and female adult fish (6-year-olds) around the reproductive period.

Arapaima gigas (paiche) is the largest scaled fish species living in the Amazon basin. Its biology is both fascinating and misunderstood. In a context of overfishing, hence reduced natural populations, aquaculture of a fish with such interesting characteristics (large size, high growth rate, no intramuscular spines) is an important issue. The development of farming production would also reduce the fishing pressure on natural populations and allow re‐stocking programmes in certain areas. To determine what factors may influence the reproductive success in captivity, data from breeding reports for 2007–2010 were collected among fish farmers in the region of Iquitos. In parallel, we carried out physicochemical measurements in different ponds where these paiches breed, and conducted personal interviews about the general fish management conditions. The results show that reproduction occurs throughout the year but with a higher intensity during the rainy season. It also highlights farms that have performed much better than others, but no single factor except feeding level has been clearly associated with reproductive success. The environmental control of reproduction in paiche, therefore, remains partly mysterious. To deepen this study, we recommend the systematic sexing of breeders, extending reproductive behavioural studies, and examining the limnological factors involved in fry mortality.

-Meal frequency is a key parameter in fish larviculture, especially in highly cannibalistic species. Knowledge of the biological bases of cannibalism (growth capacity of cannibals, morphological constraints on cannibalism, prey size preference) can help predicting the risks of cannibalism for different feeding schedules under culture conditions. This study relied on the day-by-day analysis of prey size preference and bioenergetics of individual cannibals of the catfish Pseudoplatystoma punctifer (8-65 mm standard length, SL, 0.5-400 mg dry mass, DM) at 28.5• C under 12L:12D. The results were equated with the ontogenetic variations of morphological factors (head and mouth width) and feed efficiency of larvae feeding on Artemia nauplii, in order to calculate the risks of cannibalism among fish fed 2-7 daily meals. The predation capacities of P. punctifer were highest at 8 mm SL and decreased in larger fish (largest prey = 86% and 70% SL in fish of 8 and >30 mm SL, respectively). Cannibals of increasing size preferred increasingly smaller prey relative to their own size, but also to their predation capacities. These morphological and behavioural constraints were largely compensated for by bioenergetics performance. Cannibals consumed high daily food rations (as high as 171 and 29% DM in fish <1 and >300 mg DM, respectively), exhibited high gross conversion efficiencies (0.50-0.55 and about 0.70, in fish <1 and >30 mg DM, respectively), and grew rapidly (90 and 18% DM day −1 in fish <1 and >300 mg DM, respectively). The growth advantage of cannibals over siblings fed Artemia nauplii was decisive, except for high meal frequencies (6-7 daily meals). This study supports the view that the risk of cannibalism and adequate feeding strategies can be largely predicted in a particular fish species if the morphological, behavioural and bioenergetics bases of cannibalism are examined altogether in an ontogenetic perspective.

To facilitate economical culture of black pacu, Colossoma macropomum, and red pacu, Piaractus brachypomus, in the Amazon region of South America, we assessed locally available alternative energy sources for practical diets. We tested the effects of control diets (containing wheat products) versus diets with different Amazonian feedstuffs (yucca, Manihot sculenta, plantain, Musa paradisiaca, or pijuayo, Bactris gasipaes) on the performance of the pacus in three feeding trials. Black pacu (22.5 6 0.03 g; Trial 1) or red pacu (2.56 6 0.01 g; Trial 2) were fed diets containing 30% wheat bran (control) or cooked or uncooked yucca, plantain, or pijuayo for 12 wk. In Trial 3, larger black pacu (86.9 6 6.4 g) were grown to market size in 24 wk on similar diets. Weight gain, feed conversion, survival, alternative complement activity, and lysozyme were similar among diets. Hepatosomatic index, liver glycogen, and dry matter were affected by diet in Trials 1 and 2, but effects were not consistent among trials. In Trial 3, protein efficiency ratio was lower in fish fed the diet containing wheat middlings. However, relative to wheat bran or wheat middlings, all feedstuffs tested were effective energy sources for juvenile black pacu and red pacu.

-In Amazonian fisheries, the silver arowana, Osteoglossum bicirrhosum (Cuvier 1829) is heavily exploited for human consumption as an adult, and for the aquarium trade as a small juvenile (yolk sac juvenile mainly). The periodicity of annuli formation on otoliths and growth variability of the silver arowana were studied in different river river-basins of the Peruvian Amazon between 2006 and 2009. Transverse stained sections of 606 individual otoliths were analysed from four different river-basins, the Amazonas, Ucayali, Napo and Putumayo, of which 554 could be interpreted. These belonged to 274 females ranging from 15 to 91 cm (standard length) and 280 males ranging from 30 to 91 cm. In addition, yolk sac juveniles of known age were collected to improve growth modelling. Monthly proportions of stained otolith edges validated the formation of a single annulus per year in two different river-basins with lagged hydrological cycles: the Amazonas-Ucayali and the Putumayo. Stained growth mark counts resulted in a longevity estimate of at least 16 years for the silver arowana in the Peruvian Amazon. This fish grew quickly during the first two years, and asymptotic growth was reached after four to five years, except in the Putumayo where it was reached slightly earlier. Results showed no significant growth dimorphism between sexes within basins, but indicated significant growth differences among river basins. Silver arowanas measured, on average, between 38 and 40 cm at the end of their first year. Length-at-age differences among river basins increased with age to reach over 14 cm (and >3 kg) after 7 years between the faster and slower growing populations (Amazonas and Putumayo, respectively). The growth differences observed emphasize the need for further investigation on the population structure of this species as, although these differences might merely be phenotypic responses to contrasted environmental conditions, they could alternatively reflect the existence of several populations with distinct genetic and life history characteristics. The consequences of such differences would be very important for the management and conservation of this fragile and extensively exploited species.

In Pseudoplatystoma punctifer (e.g. Pseudoplatystoma fasciatum) larvae, parental effects on hatching, growth of initial stages and dry feed adaptation were evaluated as they could influence fry heterogeneity, which is responsible for the enhancement of cannibalism, and which remains one of the main factors of mortality during larval stages. A full factorial experiment was carried out with 3 females × 3 males producing nine families of full siblings, raised separately in triplicates into 30 L tanks at 28±0.5 °C in a water recirculating system. Paternal and maternal effects were observed on hatching success, yolk utilization efficiency and growth until 26 days post fertilization. Hatching success was generally over 80% except for one male × female combination (25%). Total length (TL) at hatching and during the first 4 weeks of exogenous feeding on live Artemia nauplii and dry feeds was determined in each family using digital photographs of larvae and nih image j analysis freeware. Mean TL was calculated for each family at each sampling time and analysed using multifactorial analysis of variance tests. These results indicate not only dam but also sire effects at very early developmental stages as well as in subsequent stages of P. punctifer.

El objetivo del estudio fue determinar el efecto de tres niveles de proteína dietaria (T1=35, T2=40 y T3=45% PB) en el crecimiento de juveniles de paiche, Arapaima gigas, en un ensayo de 84 días de duración. Cuarenta y cinco alevinos de paiche (86.84 ± 15.73 g) fueron distribuidos al azar en nueve tanques de cemento recubiertos con mayólicas. Los peces fueron alimentados diariamente con una tasa de alimentación equivalente al 3% de su biomasa corporal. Se registró el crecimiento en peso y longitud en muestreos quincenales. Al termino del experimento los animales alimentados con el T2 y T3 presentaron mayor ganancia en peso y longitud que los peces del T1 (P<0.05). Al no existir diferencias significativas entre T2 y T3, se concluye que el T2 (40% PB) es el nivel proteico más adecuado para la alimentación de juveniles de paiche de 85 g de peso promedio.

The objectives of this study were the evaluation of the adaptation capabilities of re-stocked Arapaima gigas and their individual behavioural movements (males and females) to the wild environment compared to wild individuals still present in Lake Imiria, Peru and their survival rates. Using radio telemetry (external transmitters, 75 9 17 mm diameter, 35 g in air, ATS, Isanti, MN, USA), adaptation and behaviour of externally tagged, restocked cage-raised (124-143 cm TL, n = 14) and wild A. gigas (117-153 cm TL, n = 8), were monitored, focusing observations on individual behaviour and preferential localization in the lake. Home range size determined by minimum convex polygons (MCP 95 ) or Kernel Density Estimation (KDE 95 ) varied from 0.001 to around 4 km 2 , but the average KDE 50 was relatively small (0.1 km 2 ) in comparison to the tracked fish size (117-153 cm TL), indicating strong residency and presumably territoriality in this species. Also observed was that the habitat was concentrated along the shoreline of the lake and closely related to the presence of aquatic vegetation. Home range localization estimates and apparent travelled distance of wild and restocked fishes were very similar, thereby suggesting a rapid and good acclimation and survival of cultured re-stocked fish to a natural environment.