Uso comparativo de atrator luminoso e rede de arrasto na captura de larvas de peixe no estúario do Rio Formoso, Pernambuco, Brasil

Abstract

Studies on fish eggs and larvae are relevant for a thorough knowledge about fish biology and systematics, and the identification and delimitation of spawning areas. Fish larvae and many other planktonic organisms present photopositive behaviour, which makes possible their attraction and capture by using artificial lights. The objective of this study was to comparatively analyse the use of a light-attractor model and a conycal-cylindrical plankton net for collecting fish larvae, in the estuary of Formoso river, in the state of Pernambuco. Samples were taken weekly, along the different moon phases, in October-November 2003 (cycle 1), March-April 2004 (cycle 2), July-August 2004 (cycle 3) and November 2004 (cycle 4), at a fixed station in the estuary located in front of the Cruzeiro do Reduto, between the Ariquindá river estuary and Pedra beach. The light-attractor was used during different randomly ordered light periods of 0, 1, 2, 5, 10 and 20 minutes; at 10 minutes intervals between each period, while plankton towing was conducted at the beginning and end of the attractor’s use. With the light-attractor, a total of 455 fish larvae were collected, distributed in sixteen families, 21.76% of which belonged to Engraulidae, 21.10% of Clupeidae, 14.06% of Gobiidae, and 12.97% of Gerreidae, the most abundant taxa. With he plankton net, 427 larvae were sampled, within twenty families, the most abundant being Engraulidae (29.7%), Clupeidae (9.37%), Gobiidae (23.4%), Gerreidae (4.21%), Eleotridae (4.21%) and Atherinopsidae (4.45%), as well as Pleuronectiformes (4.45%). Higher larvae occurrence was recorded for the light-attractor under first quarter (27.91%) and last quarter moon (38.46%), and new moon (33,28%), for the plankton net. The light-attractor was more efficient under five minute light exposure time, when a greater abundance of larvae was recorded. The individuals sampled with plankton net were smaller than those with light attraction, what may be attributed to their escape from the net during towing. The use of light-attractor was efficient, since the individuals sampled presented a better physical fitness than those from net towing, favouring their identification. Moreover, it allowed collecting live specimens which may be cultured in the laboratory, used for growth and physiology studies, as well as obtaining ontogenic series, of extreme value for the morphological characterization and identification of early life stages of fish development.