Abstract:
Este trabalho foi realizado com o objetivo de avaliar o efeito do fotoperíodo no cultivo de larvas e juvenis do linguado Paralichthys orbignyanus. Foram realizados três experimentos (EXP1, EXP2 e EXP3), os dois primeiros compreenderam a fase larval e o terceiro a fase juvenil dos organismos. No EXP1 foram testados três fotoperíodos: 0, 12 e 24 horas de luz (hL) com duas repetições cada e duração de 5 dias. O EXP2 avaliou dois fotoperíodos: 18 e 24 hL com três repetições cada e duração de 30 dias. No EXP3 foram avaliados quatro fotoperíodos: 0, 12, 18 e 24 hL com quatro repetições cada e duração de 35 dias. No EXP1 e EXP2 foram utilizados tanques cilíndricos com fundo plano e volume útil de 10 litros, 50 larvas por litro (1 dae), sistema de água verde, primeira alimentação com rotíferos (10-25 ind/mL) seguido de náuplios de artêmia e renovação diária de 50% do meio. Para o EXP3 foram utilizados tanques cilíndricos com fundo plano, volume útil de 50 litros, fluxo contínuo, 2 juvenis por litro (35 dae), alimentados com metanáuplios de artêmia. Os resultados do EXP1 mostram proporcionalidade direta da sobrevivência (0, 1,6 e 4,5%, respectivamente para 0, 12 e 24 hL) e crescimento (3,44±0,4, 3,75±0,26 mm, respectivamente para 12 e 24 hL) com o fotoperíodo. No EXP2, a sobrevivência foi proporcional ao fotoperíodo com 4 e 13%, respectivamente para 18 e 24 hL. O crescimento foi superior em 24 hL até o início da metamorfose, após o que ocorreu uma inversão, onde o fotoperíodo de 18 hL foi significativamente (p<0,05) superior ao de 24 hL. Os dados finais de crescimento foram 12,7±1,9 e 11,6±1,4 mm, respectivamente para 18 e 24 hL. A sobrevivência final no EXP3 foi de 38,2±14; 69,2±11; 69,3±5,5 e 81±9% respectivamente para 0, 12, 18 e 24 hL. O peso final para os tratamentos de 0, 12, 18 e 24 hL no EXP3 foram respectivamente, 21,8±4,5, 114±3,7, 132,7±3,8 e 105±3,5 mg. Corroborando com os resultados do EXP2, no EXP3 o fotoperíodo de 18 hL foi significativamente superior aos demais. As larvas de linguado P. orbignyanus, podem ser cultivadas no fotoperíodo de 24 hL até os 15-20 dae. Após esta idade, a utilização do fotoperíodo de 18 hL aumenta a performance das larvas e juvenis.
The objective of this study was to evaluate the effects of photoperiod on the rearing of larvae and juvenile flounder Paralichthys orbignyanus. Three experiments were done (EXP1, EXP2, and EXP3), the first two studied the larval stage and the last the juvenile stage. In a preliminary evaluation (EXP1) three photoperiods were tested: 0, 12, and 24 hours of light (hL) with two replica each, it lasted for five days. EXP2 evaluated two photoperiods: 18 and 24 hL with three repetitions each, it lasted for 30 days. In EXP3 four photoperiods were tested: 0, 12, 18, and 24 hL with four repetitions each, it lasted for 35 days. In EXP1 and EXP2 larvae were reared in cylindrical tanks with flat bottom. Water volume was 10L, stocking density was 50 larvae/L, rotifers and artemia were offered as live prey in a green water system, 50% of the water was exchanged daily. In EXP3 juveniles were reared in cylindrical tanks with flat bottom filled with 50L of water, in a flow-through system with capacity to exchange 200% of the water daily. Metanauplii of artemia were offered as live food. Survival and growth were proportional to the photoperiod in EXP1, no survivors were observed five days after hatching in the dark (0 hL), and 1.6 and 4.5% survived in 18 and 24 hL respectively. Notochord length was equal to 3.44±0.4 and 3.75±0.3mm for 18 and 24 hL respectively. Survival in EXP2 was also proportional to the photoperiod, 4 and 13% respectively for 18 and 24 hL. Growth was higher in 24 hL during the larval stage, but as the flounder metamorphosed, those individuals reared in 18 hL achieved a better growth rate. Final length was equal to 12.7±1.9 and 11.6±1.4mm respectively for 18 and 24 hL respectively. In EXP3, survival was equal to 38±14, 69±11, 69±6, and 81±9% respectively for 0, 12, 18, and 24 hL. Final weight was equal to 21.8±4.5, 114.0±3.7, 132.7±3.8, and 105±3.5mg respectively for 0, 12, 18, and 24 hL. The results obtained in this study suggest that larval flounder should be reared with constant illumination until 15-20 days after hatching, but older larvae and juvenile will have a better performance with 18hL.
