Could a seasonal-like reduction in light radiation intensity affect cultured shrimp (Penaeus stylirostris stimpson) yield?

Abstract

Experiments were carried out to establish the effect of a simulateddecrease in daylight intensity on the yield of the cultured shrimpPenaeus stylirostris. The purpose of these experiments wasto simulate the periods in intertropical regions, which may last for severaldays, when solar radiation levels fall due to seasonal cloud cover. After 4weeks of culture, the light reduction resulted in lower shrimp yields comparedto unshaded tanks. Survival rates ranged from 54.9 to 71.1% for shaded tanksandfrom 77.0 to 83.0% for unshaded tanks. Growth rates varied between 0.091 and0.110 g.d−1 for shaded tanks and between0.189 and 0.224 g.d−1 for unshaded tanks.In unshaded tanks, variation in growth rate is related to initial shrimpstocking densities. The light reduction led to a reduced phytoplankton growthwith, as a consequence, an increase in the concentration of dissolved mineralnitrogen [(NO3 − +NO2 −)-N,(NH4 ++NH3)-N] and dissolved organicnitrogen (DON). The higher mortality and lower growth observed in the shadedtanks cannot be entirely explained by the concentrations of mineral nutrients,the temperature, the pH or the O2 concentration. The lower resultsobtained with the shaded tanks could be most likely a consequence of thetoxicity of dissolved organic matter.