Reproductive biology of the armoured catfish Loricariichthys castaneus (Castelnau, 1855) in Lajes reservoir, southeastern Brazil

Sex ratio, gonadal development, breeding season and fecundity of the armoured catfish Loricariichthys castaneus were described to assess its reproductive strategy in a Brazilian tropical reservoir. In total, 226 specimens (199 females and 27 males) were captured from September 2005 to August 2006 and examined in the laboratory. Females outnumbered males and achieved sizes larger than 330 mm TL. Oocyte development, determined by histological analysis, was asynchronous with oocyte size, ranging from pre-spawning (27-270 mu m) to spawning (243-3460 mu m), followed by a sharp decrease in the mean oocyte diameter postspawning (590-730 mu m) as the spawning proceeded. Spawning occurred throughout most of the year, peaking in August-September and reaching a low in April-May, according to variations in GSI and frequencies of stages of gonadal development. Batch fecundity ranged from 242 to 833 vitellogenic oocytes (relative fecundity = 2.27 oocytes g(-1)), averaging 483 oocytes, and was positively related to gonad weight (P = 0.00003). Oocyte diameters ranged from 0.027 to 5.59 mm, with vitellogenic diameters ranging from 2.08 to 5.59 mm. Continuous development of oocytes throughout the year suggests that L. castaneus presents indeterminate fecundity and is a batch-spawner. These attributes, associated with parental care and a wide reproductive period, correspond to an equilibrium strategy that has proved to be effective in the Lajes reservoir.