AGE AND GROWTH OF THE MARINE CATFISH, 

 NETUMA BARBA (SILURIFORMES, ARIIDAE), IN THE ESTUARY OF 



THE PATOS LAGOON (BRASIL) 1 



Enir Girondi Reis 2 



ABSTRACT 



Otolith cross sections from Netuma barba were used for age and growth determinations. There is close 

 agreement between average back-calculated lengths and average observed lengths determined from 

 otoliths at capture for each year class. One opaque and one hyaline zone is formed annually. The hyaline 

 zone appears to be formed during the breeding season when the estuarine mature population is scarcely 

 feeding. Von Bertalanffy growth parameters were estimated through Beverton's method which showed 

 the smallest residual variance between observed and calculated lengths for year class. The growth equa- 

 tion (mm) is Lt = 638 [1 - exp (-0.1287(f + 0.195))]. The largest specimen observed was a 980 mm 

 female, 36 years old. The life span of N. barba was estimated to be 23.1 years and the natural mortality 

 rate 0.13. 



The sea catfish, Netuma barba (Lacepede 1803), 

 ranges in the western Atlantic from Bahia (lat. 

 17°00'S) in Brasil (Gunther 1864) to San Bias (lat. 

 40°32'S) Argentina (Lopez and Bellisio 1965). It is 

 the second most important estuarine fishery re- 

 source in the Patos Lagoon and is caught with gill 

 nets (Reis 1982a). The species accounts for about 

 29% of the total fish landings in the estuary from 

 October to December, a period when it migrates 

 from the sea to spawn. During the remaining 

 months the species is dispersed in low abundance 

 in the ocean (Reis in press). Observations on Netuma 

 barba in Brasil have been restricted to taxonomy 

 (Higuchi et al. 1982) and to feeding and reproduc- 

 tion (Ihering 1888, 1896; Nomura and Menezes 1964; 

 Reis in press). 



Age determinations in catfishes are usually based 

 on reading vertebrae and pectoral or dorsal spines 

 (Pantulu 1962; Tweddle 1975). Pectoral spines of 

 Netuma barba were not used in the present study 

 because they showed inconsistencies in age deter- 

 mination. However, a preliminary investigation 

 revealed the presence of clear and readable zones 

 in otoliths. This paper deals with the interpretation 

 of these zones, the possible causes of zone forma- 

 tion, and the determination of growth of Netuma 

 barba in the estuary of the Patos Lagoon. 



'Based on a thesis in partial fulfillment of the requirements for 

 the MS degree, Fundacao Universidade do Rio Grande - Rio Grande 

 (Brasil). 



2 Departamento de Oceanografia, Fundacao Universidade do Rio 

 Grande, Caixa Postal 474, 96200 - Rio Grande - RS, Brasil. 



MATERIALS AND METHODS 



Study Area 



The Patos Lagoon, the largest lagoon system in 

 southern Brasil (10,360 km 2 ), is connected to the 

 Atlantic Ocean by a narrow access canal (Fig. 1). 

 The estuary of the lagoon serves as a breeding, 

 nursery, and feeding ground for most of the coastal 

 fish which migrate through the canal and represent 

 a significant percentage of the national fishery 

 resource. 



Collections of adult Netuma barba were made 

 from fish-processing plants located in the estuarine 

 zone of the lagoon, off the coast of Rio Grande to 

 Sao Lourenco do Sul, a town located 94 km inland 

 (Fig. 1). Juveniles were collected by special research 

 surveys carried out in the estuary. Data were col- 

 lected from September 1977 to December 1980 on 

 4,120 specimens. No samples were available from 

 January to March because of a closed fishing season 

 of Ariidae in the area, and few samples were col- 

 lected from April to July due to the absence of the 

 species in the estuary. 



Sampling Procedure 



Specimens were measured (total length, mm), 

 weighed (g), and sexed. Lapillus otoliths were re- 

 moved, sectioned transversally next to the nucleus, 

 polished, and were examined under a 10 x binocu- 

 lar microscope. The dorsal, polished half of the 

 otoliths was observed with transmitted light. The 



Manuscript accepted January 1986. 

 FISHERY BULLETIN: VOL. 84, NO. 3, 1986 



679 



