REIS: AGE AND GROWTH OF MARINE CATFISH 



barba is supported by the following: 1) one opaque 

 and one hyaline zone is formed annually (Figs. 3, 

 4); 2) a gradual decrease of length increments with 

 age (Table 1); 3) observed lengths generally agree 

 with back-calculated lengths (Fig. 5); and 4) distri- 

 bution of back-calculated lengths for previous ages 

 shows similar modes for each year class (Fig. 6). 



Length-weight Relationship and 

 Condition Factor 



A total of 685 specimens captured during 1980 

 was used to compute the length-weight relationship 

 for each sex: 



Male Wt = 4.70 x 10" 6 Lt 3u 



Female Wt = 2.19 x 10" 6 Lt 326 



Total Wt = 4.41 x 10" 6 Lt 315 



r = 0.992 n = 332 

 r = 0.952 n = 363 

 r = 0.987 n = 685 



The analysis of covariance (Snedecor and Cochran 

 1970) at P < 0.05 level showed significant difference 

 only for the \i value, and for that reason condition 

 factor (K) was determined for each sex. There is a 

 decrease of mean K values towards the end of the 

 year (Fig. 7). The condition factor for males is 

 always higher probably due to a more intense feed- 

 ing prior to reproduction. Low K values reveal the 

 stress the fish suffers when it is scarcely feeding and 

 fat reserves are being diverted to gonad maturation 

 (Reis in press), thereby causing a cessation of 

 growth. I proposed that K values for males will 

 sharply decrease after spawning due to an oral in- 

 cubation period that lasts 1 to 2 mo and prevents 

 males from feeding (Reis in press). 



Calculation of Growth 

 Parameters 



cr 

 o 



t- 



z 

 o 



Q 



Z 



o 

 o 



cc 

 o 



b. 



O 



o 



fl 8 



fl 



ft 



MALES 



& 



m 



hlO o 

 m 



z 



H 

 O 

 I 

 I> 



10 



34 35 



54 66 



56 



44 



FEMALES 



m 



3J 

 O 



o 



i 

 > 



10? 



26 



H 

 SEPT. 



36 48 



I TC 



OCT. 



72 85 



X JL 



NOV. 



32 



X 



68 n 

 DEC. MONTH 



Figure 7.—K condition factor and percent change for males and 

 females of Netuma barba related to time (n = number of specimens; 

 I = first half of the month; II = second half of the month) 



Von Bertalanffy growth parameters were esti- 

 mated by Beverton's (1954) method which presented 

 the smallest residual variance between observed and 

 calculated lengths for year class on the ages that 

 are most affected by gear selectivity (8-12 yr old). 

 For fish populations captured from a certain age on- 

 ward, the smallest residual variance should be 

 sought for all year classes from age at first capture. 

 For Netuma barba the smallest residual variance 

 could not be ascertained by this method because the 

 true length distribution is unknown due to the use 

 of gillnets as fishing gear. Growth equation for age 

 1 to 12 for both sexes in represented by 



Lt = 638 [1 - e -o.i287(t + o.i95)]_ 



Figure 8 shows both calculated and observed lengths 

 for each year class. 

 Growth in weight for each sex resulted in 



Male 

 Female 



Wt = 2981.89 [1 - e-°- 1287 < e+0 - 195) f u 



Wt = 3035.70 [1 - e-0.128W + 0.195)]3.26 



-500 



E 

 ^400 



o 



-I 



300 



_>200 

 2100- 



S 



.^" 



Loo=638nrn * * Colculoted Ltngtht 



K =0,1287 . _ Observed Length* 



I 2 3 4 5 6 7 8 9 10 II 12 

 ESTIMATED AGE 



Figure 8.— Growth curve of Netuma barba. 



685 



