This experiment evaluated the efficacy of benzocaine to reduce stress response during transport of juvenile cobia. Fish (30 g) were packed in bags and transported for 8 h (stocking density = 10 g L-1). Three concentrations of benzocaine were evaluated: 0, 2, and 6 mg L-1. Blood samples were taken for glucose and hematocrit before transportation, and then at 0, 2, 24, and 48 h after. Water quality parameters were verified. No mortality was observed. Total ammonia nitrogen was higher (2.46 mg L-1) and pH was lower (6.92) at 2 mg benzocaine L-1. There was an increase in blood glucose for all treatments on arrival, and it was higher for those exposed to benzocaine at 6 mg L-1, although at 48 h they were all similar. The hematocrit did not differ among treatments. The results suggest: 1) the density 10 g L-1 is considered safe for juvenile cobia transport; 2) benzocaine did not mitigate stress response on cobia during transport, therefore its use is not recommended for this purpose.

En este experimento se evaluó la eficiencia de la benzocaína para reducir la respuesta al estrés durante el transporte de juveniles de cobia. Los peces de 30 g se almacenaron en bolsas y se transportaron durante 8 h (densidad de almacenaje = 10 g L-1). Se evaluaron tres concentraciones de benzocaína: 0, 2 y 6 mg L-1. Se tomaron muestras de sangre para glucosa y hematocrito antes del transporte y después de 0, 2, 24 y 48 h. Se verificaron los parámetros de calidad de agua. No se observó mortalidades. La concentración de amoníaco total fue alta (2,46 mL-1) y el pH fue bajo (6,92) a 2 mg de benzocaína L-1. Al término del transporte se determinó un aumento de glucosa en la sangre en todos los tratamientos, siendo mayor en los peces expuestos a 6 mg de benzocaína L-1, aunque a las 48 h todos fueron similares. El hematocrito no mostró diferencias entre los tratamientos. Los resultados sugieren que: 1) la densidad de10 g L-1 es segura para el transporte de juveniles de cobia; y 2) la benzocaína no redujo la respuesta de estrés en cobia durante el transporte, por lo tanto no se recomienda su uso para este propósito.

RESUMO No presente estudo foi realizada uma análise ontogenética dos órgãos imunocompetentes do bijupirá até 53 dia após a eclosão (dae) com técnicas histológica e imunohistoquímica. O rim foi o primeiro órgão linfohematopoiético a aparecer, ao 1 dae, seguido pelo baço aos 5 dae e pelo timo aos 7 dae. Os primeiros receptores CD3 em linfócitos foram observados em 27% no tecido do timo aos 7 dae e 99% aos 53 dae. A expressão fenotípica de receptores de CD3 foi registrada em 10% do rim aos 8 dae e em 32% aos 53 dae. Os receptores CD4 foram observados em 5% e 63% da área do timo aos 7 e 53 dae, respectivamente. No rim, linfócitos T4 foram primeiramente observados aos 13 dae em 9% do órgão e em 28% aos 53 dae, definindo o desenvolvimento funcional do sistema específico associado com a capacidade de memória imunológica.

ABSTRACT In the present study was evaluated the ontogenic of immunocompetent organs of cobia up to 53 days after hatching (dah) through histology and immunohistochemistry techniques. The kidney was the first lymphohematopoietic organ to appear, at 1 dah, followed by the spleen at 5 dah and the thymus at 7 dah. The first CD3 receptors on the lymphocytes were observed in 27% of the thymic tissue at 7 dah and in 99% at 53 dah. The phenotypic expression of CD3 receptors was registered in 10% of the kidney at 8 dah and in 32% at 53 dah. CD4 receptors were observed in 5% and 63% of the thymic area at 7 and 53 dah, respectively. In the kidney, T4 lymphocytes were first observed at 13 dah in 9% of the organ and in 28% at 53 dah, defining the functional development of the specific system associated with immunological memory capacity.

Cobia (Rachycentron canadum) is a marine finfish with good potential for mariculture. This study analyzes the effects of probiotic Bacillus spp. on the performance of cobia larvae reared in a recirculating aquaculture system (RAS). Larvae were stocked into two independent RAS for 26 days after hatching. One of the systems (Probiotic treatment) received the addition of a commercial probiotic consisting of B. subtilis, B. licheniformis and B. pumilus directly into the water and by live feed. Survival, final weight and water quality were not affected by probiotics. Results showed larvae of the probiotic treatment demonstrated a greater resistance to salinity stress. Immunohistochemical analysis showed a higher expression of CD4 in probiotic treatment. These results suggest that Bacillus spp. probiotics used in RAS have a potential stimulating impact on immune system differentiation and increases salinity stress resistance of cobia larvae.

Cobia (Rachycentron canadum) es una especie de pez marino con buen potencial para la maricultura. Este estudio analiza los efectos del probiótico Bacillus spp. sobre el desempeño de las larvas de cobia criadas en un sistema de recirculación de agua (RAS). Las larvas fueron sembradas en dos RAS independientes durante 26 días después de la eclosión. Uno de los sistemas (tratamiento experimental) recibió la adición de un probiótico comercial que consiste en B. subtilis, B. licheniformis y B. pumilus directamente en el agua y por alimento vivo. La sobrevivencia, peso final y calidad del agua no se vieron afectados por los probióticos. Los resultados mostraron que las larvas del tratamiento probiótico presentaron una mayor resistencia al estrés por estrés salino. El análisis inmunohistoquímico mostró una mayor expresión de CD4 en el tratamiento probiótico. Estos resultados sugieren que estos probióticos utilizados en las larvas de cobia en RAS tienen un potencial impacto estimulante sobre la diferenciación del sistema inmunológico y aumenta la resistencia al estrés de las larvas de cobia.

O objetivo deste estudo foi descrever a ontogenia dos folículos da tireóide em Rachycentron canadum. Larvas foram coletadas diariamente (n= 15 – 20) desde a eclosão até 15 dae (dias após eclosão). Posteriormente foram coletadas a cada dois dias até o 28 dae; uma nova amostragem ocorreu aos 53 dae. As larvas foram desidratadas e emblocadas em Paraplast e secções de 3 µm foram desparafinadas, reidratas e coradas com HE e PAS. Um folículo estava presente ao 1 dae e três foram encontrados aos 8 dae. O número de folículos aumentou até 19 aos 53 dae. O diâmetro dos folículos e a altura das células foliculares foram menores ao 1dae (68,3 ± 1,00 e 4,6 ± 0,01 µm), mas aumentou a partir do 8 dae (24,03 ± 0,46 µm e 6,43 ± 0,46 µm). A partir do 8 dae a presença de vesículas de reabsorção foi observada no colóide e a partir de 19 dae alguns folículos não apresentaram colóide. O surgimento precoce do folículo da tireóide no bijupirá assim como a grande quantidade de folículos sem colóide e/ou com a presença de vesículas mesmo após a metamorfose podem ser a explicação do rápido crescimento da espécie.

The aim of this study was to describe the ontogeny of thyroid follicles in cobia Rachycentron canadum. Larvae were sampled daily (n=15 - 20) from hatching until 15 dah (days after hatching). Following, larvae were sampled every two days by 28 dah; a new sample was taken at 53 dah. The samples were dehydrated, embedded in Paraplast, and sections of 3 µm were dewaxed, rehydrated and stained with HE and PAS. A single follicle was already present 1 dah and three follicles were found 8 dah. The number of follicles increased up to 19 on 53 dah. The diameter of follicles and follicular cell height were lower 1 dah (6.83 ± 1.00 and 4.6 ± 0.01 µm), but increased from 8 dah (24.03 ± 0.46 µm e 6.43 ± 0.46 µm). From 8 dah, the presence of reabsorption vesicles was observed in the colloid and from the 19 dah some follicles did not present colloid. The early thyroid follicle appearance in cobia larvae as well as the high quantity of follicles without colloid and/or with vesicles even after the metamorphosis, might be the explanation of the fast growth of the cobia.