Spawning calls by zulega, Prochilodus argenteus, a Brazilian riverine fish

Abstract

We studied calling and spawning of the potamodromous fish zulega (Prochilodus argenteus, Prochilodontidae) in the Sao Francisco River (SFR), Brazil. The study reach was the 143 river km (rkm) downstream from Tres Marias Dam (TMD), but most effort was at the Pontal spawning ground (PSG). PSG is located in the SFR at the mouth of the first major tributary (Abaete River), 33 rkm downstream from TMD. Abiotic factor in the flooding by the Abaete River due to rain was the major trigger for spawning by zulega at PSG. Size of PSG increased with magnitude of Abaete River flooding. Zulega males called 24 h a day, but longer periods of calling occurred in the daytime than at night. Zulega males called in lek choruses, apparently in discrete arenas, and did not school while calling. Spawning calls from zulega occurred in the entire 110 rkm reach of the SFR downstream from PSG, but only during major flooding from the Abaete River. The spawning trigger factor was absent in SFR water draining from TMD. A large spillage of 1700 m3*s−1 from this dam that was warmer than temperatures during zulega spawning inhibited spawning possibly due to alteration of the thermal regime of the Sao Francisco River. The best time for spillage to restore zulega fisheries downstream of TMD may be in the decreasing phase of a natural flood, but further tests are needed. Damming the Abaete River may eliminate the spawning trigger for zulega at PSG and downstream in the SFR.