FISHERY BULLETIN: VOL. 84, NO. 3 



agreement between observations increased to 

 79.9%. 



Time of Zone Formation 



The percentage of hyaline and opaque edged oto- 

 liths was plotted for each month (Fig. 3). Otoliths 

 showing hyaline edge are more abundant in Decem- 

 ber when they comprise 63.7% of the total; opaque 

 edged otoliths are fewer in this month (33.9%). Stu- 

 dent's £-test (Snedecor and Cochran 1970) showed 

 that proportions between hyaline and opaque edged 

 otoliths differ significantly (P < 0.05) for most 

 months (Fig. 3). Also, the mean width of the opaque 



zone on the otolith edge decreased towards the end 

 of the year (Fig. 4), indicating a recent hyaline zone 

 formation. The period of zone formation is not the 

 same for all individuals, the result of individual 

 growth differences. It is evident, however, that only 

 one hyaline and one opaque zone is formed each 

 year. Formation of slow-growth zones during warm 

 months in Netuma barba coincides with the spawn- 

 ing period and the cessation of feeding activity (Reis 

 in press). Both events suggest a decrease or a pause 

 in growth when hyaline zones are formed. Menon 

 (1953) observed that decreased feeding and gonad 

 maturation may cause a periodic formation of the 

 growth marks in skeletal parts of fish. During the 



too 



90 



80- 

 j 70 



Ul 



60 

 ui 



ec 



"■ 50 

 ui 



«* 40 



§ 30 

 e 



Ul 



01 20 



10 



/ \ 

 / \ 

 / \ 





— HYALINE EDGE 

 -x OPAQUE EOGE 



155 2W 179 

 OCT. NOV. DEC. 



1977 



48 74 22 12 75 42 73 44 



APP..MAY.JUN. JUL. AUG. SEPT. OCT. NOV.DEC. 



1978 



35 23 76 82 67 

 AUG.SEPTQCT. NOV DEC. 



1979 



65 175 251 200 n 



SEPT.OCT.NOV. DEC. MONTH 



1980 



Figure 3.— Percentage of hyaline and opaque edge on otoliths of Netuma barba related to the months of four years (* P < 0.05; n = 



number of specimens). 



z 

 o 



N 



4- 



o 

 o 



ui 



X 



X 



\- 

 o 



MALES 



t 



SEPT. 



55 



— i — 

 OCT. 



101 



ft 



80 



ft 



FEMALES 



fl 



26 



71 



NOV. 



DEC. 



T 



SEPT. 



OCT. 



141 



— I — 

 NOV. 



94 n 



— i 



DEC. MONTH 



Figure 4.— Mean width and confidence limits at P < 0.05 level of the last opaque zone 

 on otolith's edge for males and females of Netuma barba (n = number of specimens). 



682 



