2 
ABSTRACT 
Cynoscion jamaioensis (Vai lTant  & B ocour t )  undergoes  a  b io logical  cycle  
which i s  l inked tb , the  annual  changes  in  the  environment ,  de termined 
la rge ly  by the  inf luences  of  the  Orinoco River .  The ef fec t  of  the  Orinoco 
decreases  wi th  d is tance  resul t ing  in  d i f ferences  in  the  t iming of  some 
events ,  such as  spawning and annulus  format ion,  in  the  di f ferent  sampl ing 
a reas .  Peak spawning takes  p lace  dur ing February  and March but  lower  
levels  of  spawning cont inue  over  an  ex tended period .  Juveni les  a re  
recru i ted  in to  the  f i shery  throughout  the  wet  season and these  f ish  mature  
a t  the  end o f  the  f i r s t  year  o f  growth .  The major  par t  of  the  d ie t  of  
th is  species  cons is t s  o f  a  re la t ively  smal l  number  of  prey species ,  indicat ­
ing a  grea ter  se lec t iv i ty  of  feeding than has  been found fo r  members  of  
the  genus .  Fish  were  success ful ly  aged and i t  was  found that  Age 0  f i sh  
const i tu te  the  major  par t  of  the  popula t ion .  Due to  the  ex tended spawning 
and recrui tment  and the  reduct ion in  growth a f ter  the  f i r s t  year ,  there  i s  
a  great  degree  o f  over lap  of  the  year  c lasses .  In  the  a reas  sampled the  
percentage  of  males  increases  wi th  age,  indica t ing e i ther  a  d if fe rent ia l  
sex morta l i ty  or  sexual  segregat ion .  A g reater  number  of  males  are  found 
off  the  nor th  coast  than are  found in  the  Gulf .  Length /Weight  re la t ionsh ips  
and the  von Ber ta lanffy  growth constants  are  evalua ted.  I t  appears  tha t  
the  local  populat ion of  C. jamaioensis  i s  not  an  i sola ted  one.  There  i s  
probably  some l inkage wi th  the  Venezuelan popula t ion .