In carnivorous fish species, zooplankton is one of the main food items in the early life stages and some fish species continue feeding on such food items further along the life stages even in the farming environment. In this study, the intake of natural food items was assessed in juvenile pirarucu Arapaima gigas reared in earthen ponds. Juvenile pirarucu (12.2 ± 4.32 g and 12.1 ± 1.13 cm) were stocked in fertilized earthen ponds (240 m²). For the analysis of the fish stomach content and plankton in the pond water, the fish and pond water were sampled weekly for 75 days and biweekly until the fish reached a mean weight of 750 g. Although artificial feed was used, pirarucu also ingested the natural food available in the pond water. Among the zooplankton, pirarucu demonstrated feeding preference for cladocerans despite the abundance of rotifers and copepods. Cladocerans were present in more than 80% of the stomach contents of fish up to 300 g and in 65%, 45% and 17% of fish of 301–500 g, 501–700 g and 701–900 g respectively. Copepods were present only in fish up to 500 g at low abundance. High ingestion of insects and plant material was observed in the stomach content of fish of all size classes. The results demonstrate that juvenile pirarucu ingest natural food available in the farming pond and suggests that the adoption of pond fertilization practices may have positive effects on fish growth performance.

The loading density of pirarucu Arapaima gigas transported for 6 hr in open system was assessed on survival, physiological parameters (blood hematocrit, cortisol, lactate and glucose concentrations) and water quality (temperature, pH, ammonia, dissolved oxygen and carbon dioxide). No mortality was observed after fish transportation at 80, 120 and 160 kg/m³, although ammonia and carbon dioxide concentrations increased and dissolved oxygen decreased. Physiological parameters were not affected by loading density but significant differences were observed between sampling periods (immediately before transport, immediately after transport, 24 and 96 hr after transport), except glucose. Hematocrit values increased with time, whereas lactate concentration decreased. No significant differences were observed in blood cortisol levels before and after transport, but concentration increased gradually for 96 hr after transport. According to the results, 9 kg pirarucu may be transported for up to 6 hr at a loading density of 160 kg/m³. K E Y W O R D Sair-breather, Arapaima gigas, flow-thru system, stress, transport container

The lack of tools for sex identification and assessment of gonadal development are hindering our ability to study the reproductive dysfunction of Arapaima gigas in captivity. This study initially aimed to validate a non-surgical endoscopy procedure to identify sex in juveniles and assess stage of ovary development in female broodstock under field operational conditions. Cannulation, assisted through the description of the genital anatomy, made ovarian biopsy possible to describe oocyte development from primary growth to pre-ovulation, providing a first classification scheme for oogenesis in the species including description of the micropyle morphology using scanning electron microscopy. Cannulation was also successfully performed without endoscopic guidance, which allowed monitoring of the ovarian development along the reproductive season together with profiling of plasma sex steroids (17β-oestradiol (E 2) and 11ketotestosterone (11-KT) in females and males respectively). The monitoring of our study population showed females paired with males in earthponds sexually matured and reached oocyte maturation during the spawning season. However, since no spawning was recorded, eggs had either been resorbed or released and not fertilized by the male. Plasma E 2 levels remained high in females, as expected in an asynchronous species during the spawning season with multiple batches of oocytes being recruited. Plasma 11-KT showed a tendency to decrease suggesting a male reproductive dysfunction or the end of the reproductive season with a lack of synchronisation between genders. In conclusion, endoscopy and cannulation are tools that can be promptly applied to aid sex identification, assessment of reproductive function and overall broodstock management in wild and captive stocks. These tools will greatly help future studies looking at the effects of environmental, social and hormonal cues on reproductive development with the aim to develop a spawning induction protocol for the species. Body of text The Pirarucu Arapaima gigas is a dioic and iteroparous species without evident sexual dimorphisms (Chu-Koo et al., 2009). Like salmonid and anguillid species, the ovary of A. gigas lacks an external capsule (gymnovarium), meaning mature oocytes are directly released into the coelomatic cavity before reaching the gonopore at spawning (Grier et al., 2009; Godinho et al., 2005; Colombo et al., 1984). However, the gonopore morphology and position have not been described, which hindered the practice of cannulation (Núñez et al., 2011; Chu-Koo et al., 2009). This is a major constraint to the study of reproductive function in the species for both wild and captive stocks (Torati et al., 2016; Núñez et al., 2011), as assessment of reproductive condition can only rely on sacrificing animals to sample gametes, which contrasts with conservation efforts. Consequently, data on gonadal development, oocyte maturation, ovulation, and spawning rhythms is still scarce (Godinho et al., 2005; Núñez and Duponchelle, 2009) as for data on spawning rhyth...

Because sex ratio in the broodstock can influence the reproductive behaviour of a species, the influence of sex ratio on the reproductive success of pirarucu, Arapaima gigas, in captivity was assessed. Pirarucu breeders were stocked in 0.10-0.13 ha earthen ponds at three sex ratios in quadruplicate: one male to one female (1M1F); one male to two females (1M2F); and two males to one female (2M1F). Eight spawning events occurred, seven of them with the 1M1F sex ratio, which was the most successful of the three tested sex ratios. KEYWORDS: breeding pairs, mating, tropical fish cultivationInfluência da proporção sexual na reprodução do pirarucu, Arapaima gigas, em cativeiro RESUMO A proporção sexual de reprodutores pode influenciar o comportamento reprodutivo de uma espécie. Em função disso, avaliouse o efeito da estocagem de reprodutores em diferentes proporções sexuais no sucesso reprodutivo do pirarucu, Arapaima gigas, em cativeiro. Reprodutores foram estocados em viveiros de 0,10-0,13 ha, distribuídos em três tratamentos (proporções sexuais), com quatro repetições cada: (1M1F) um macho e uma fêmea, (1M2F) um macho e duas fêmeas; e (2M1F) dois machos e uma fêmea. Foram observadas oito desovas, sendo a proporção sexual 1M1F a mais eficiente, apresentando sete desovas. Sugere-se, portanto, que a proporção sexual de um macho para cada fêmea é mais adequada para a reprodução do pirarucu em cativeiro. PALAVRAS-CHAVE

We assessed the effect of stocking density on physiological parameters (blood lactate, glucose, cortisol, hematocrit), water quality (temperature, dissolved oxygen, pH, unionized ammonia, carbon dioxide), and survival during the transportation of fingerling (24.5 ± 4.7 g) and juvenile (615.8 ± 122.2 g) pirarucu (Arapaima gigas) for six hours in plastic bags. The tested densities were 65, 80, 95, 110 and 125 g L-1 for fingerlings, and 50, 80, 110, 140 and 170 g L-1 for juveniles (three replicates each). Parameters were measured prior to and immediately after transportation, and at 24 and 96 hours recovery after transportation. No mortality was observed, except for fingerlings (< 3%) at densities of 110 and 125 g L-1 during recovery. All the water quality parameters were significantly altered after the transportation of fingerlings and juveniles. Water temperature, dissolved oxygen, carbon dioxide and unionized ammonia increased, but pH decreased. Only carbon dioxide and unionized ammonia differed among densities. Cortisol levels did not increase over time, except for the juveniles at 170 g L-1, which still had high cortisol after 96 hours. Glucose significantly increased after transportation for all the treatments and returned to the initial values during the recovery period. Conversely, the lactate values were still high after 96 hours. Hematocrit was assessed only for juveniles and was significantly lower after transportation. We conclude that fingerling and juvenile pirarucu can be safely transported at densities up to 95 g L-1 and 140 g L-1, respectively.