Population structure of the thomas sea catfish, notarius grandicassis (valenciennes, 1840 [siluriformes: ariidae]), caught on the western coast of the state of maranhão, Brazil

The Thomas sea catfish, Notarius grandicassis, belongs to the family Ariidae and is one of the most exploited species on the western coast of the state of Maranhão, Brazil. The scarcity of studies on this fishing resource underscores the need for information on the population structure and biological aspects of the species. The aim of the present study was to collect information on the population structure and condition factor of N. grandicassis. Specimens were collected during campaigns on the western coast of Maranhão (01º 02’ to 2º 10’S and 45º 58’ to 44º 21’W) from April 2012 to August 2013 using drift gillnets. In the lab, total length (Lt), total weight (Wt), and gonad differentiation were determined for each individual. These data were processed to acquire population structure and reproduction parameters. The sample was composed of 499 individuals (85 males and 414 females); the largest (69 cm) and smallest (27.4 cm) individuals were both females. The highest frequency of captured individuals was in the 42.4 to 47.4 cm class interval. The weight/length relationship revealed a type of positive allometric growth, with Wt = 0.0056 Lt3.07 for males and Wt = 0.0066 Lt3.02 for females. The relative condition factor revealed the same pattern for both sexes in April 2012 and May 2013, demonstrating better conditions in this period.