Desenvolvimento dos órgãos linfoides de larvas de pacu (Piaractus mesopotamicus) em resposta a diferentes manejos alimentares

The development of the lymphoid organs in pacu larvae (Piaractus mesopotamicus) since hatching until 34 days of age and the effects of different feeding protocols on the morphogenesis of the immune system and the resistance of ar exposure were investigated. The feeding treatments studied were: (TP) early weaning, replacement of artêmia nauplii by commercial microdiet initiated at eight days after the first feeding; (TT) late weaning, replacement initiated at 15 after the first feeding; (ART) larvae fed exclusively artemia nauplii. The histological samples to describe the ontogeny of the kidney, thymus and spleen were taken twice a day until 13 days pos-hatch (dph), once a day until 16 dph and then each three days until the end of the experiment. On the first feeding day, 7, 11, 16, 22 and 30 days after the beginning of the active feeding, biometrics were made. A stress resistance test (air exposure for 1, 3, 5, 7 e 20 min) was applied to the larvae 12 days after the end of the early and late weaning, respectively, after 22 and 29 days of feeding. The histogenesis of the lymphoid organs demonstrated that the fisrt organ to became lymphoid was the thymus with 2 dph, although the kidney had been observed since the moment the larvae hatched. At 6 dph, the kidney show signs of differentiation. The spleen was the last organs to appear at 6 dph. At 35 dph the kidney had already differentiated into head kidney (with monocytes, lymphocytes and hematopoietic tissue) and posterior kidney (renal tubules). The thymic parenchyma didn't present differences, however the cells differentiated in the inner and outer zones and the spleen did not present differentiation between red and white pulp until this period. Comparing to the treatment that received only artemia nauplii, early and late weaning reduced de survival of the larvae. However, only the early weaning decreased the specific growth rate and weight gain and caused difference on larvae size ...O desenvolvimento dos órgãos linfoides de pacu (Piaractus mesopotamicus) desde a eclosão até 34 dias de vida, e os efeitos de diferentes manejos alimentares sobre a ontogenia do sistema imunológico e a resistência das larvas à exposição ao ar foram avaliados neste estudo. Os manejos alimentares estudados foram: (TP) transição prematura de náuplios de artêmia para a dieta comercial iniciada aos oito dias após a primeira alimentação (12 dias pós- eclosão); (TT) transição tardia de náuplios de artêmia para dieta comercial iniciada aos 15 dias após a primeira alimentação (19 dpe) e (A) alimentação exclusivamente com náuplios de artêmia. As amostras para análises histológicas para descrição da ontogenia do rim, timo e baço foram tomadas duas vezes por dia, diariamente até os 13 dias pós-eclosão (dpe) (nove dias pós a primeira alimentação), uma vez ao dia até o 16 dpe (12 dias após a primeira alimentação) e, posteriormente, a cada três dias até o final do experimento. Biometrias foram realizadas na primeira alimentação, aos sete, 11, 16, 22 e 30 dias após o início da alimentação exógena. Um teste de resistência ao estresse (exposição ao ar por 1, 3, 5, 7 e 20 min) foi aplicado às larvas após 12 dias do término da transição alimentar prematura e tardia, respectivamente aos 22 e 29 dias de alimentação. A histogênese dos órgãos do sistema imune do pacu mostrou que o primeiro órgão a se tornar linfoide foi o timo aos 2 dpe, embora nos rins tenham sido observadas células indiferenciadas desde a eclosão. No início da alimentação exógena, aos 5 dpe, o rim da larva de pacu apresenta pequenos linfócitos e células eritropoiéticas dispersas entre os túbulos renais. O baço foi último órgão a se tornar linfoide, sendo observado a partir do 6º dpe como um órgão eritrocítico e, a partir do 16º dpe, o órgão torna-se linfoide. Ao final do experimento, com 34 dpe, o rim...Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Stocking density for arapaima larviculture

Inadequate stock density in fish larviculture can cause a dominant behavior that harms feeding and results in stress, lots of heterogeneous fish and low productive rates. This study aimed to evaluate the effect of stocking densities on growth performance, cortisol levels and arapaima (Arapaima gigas) larvae production cost. Arapaima larvae (1.32 ± 0.25 g; 5.90 ± 0.33 cm) were used and stocked at densities of 400, 800, 1200, 1600 and 2000 larvae m−3. Fish were housed in 15 tanks (50 L) according to a completely randomized design in a recirculating water system with constant aeration. Larvae were fed an extruded commercial diet (45% crude protein) at the 10% biomass proportion, divided into six meals day−1 for 30 days. At the end of the trial, fish were measured and weighed, and four fish per tank were euthanized to analyze plasma cortisol. The arapaima larvae production cost was calculated for all the stocking densities. The fish reared at the 2000 larvae m−3 density presented feeding voracity and the best zootechnical performance: final weight (12.16 ± 0.89 g), weight gain (10.84 ± 0.89 g), relative growth rate (7.69 ± 0.26%) and lower stress levels, which resulted in a 93.33% survival rate. This group of fish presented a low production cost and, consequently, the highest income per larva (2.34 US$). For arapaima larviculture, using 2000 larvae m−3 is recommended because it results in higher growth, more homogeneous fish, better survival rates which, in turn, result in the lowest arapaima larvae production cost. © 202