FISHERY BULLETIN: VOL. 87, NO. 3, 1989 



General Behavior 



Swimbladder (SB) 

 and Osteology 



Free Neuromasts 



Vision 



Hatch 



Distribution More Demersal 



Juvenile Stage 



100 



Cannibalism -» 



Ule Y-S/Flrst-Feedlng 



Notochord Fltxlon 



-+- 



-f- 



Flexion Compitt* 



SB Pr«a«n(, 

 Not lnllal*d 



Full Inriallon 

 otSB 



5-7 Pair On Htad ft Trunk 



ParllBJlO & SO. 

 Rowt On H«Bcl 



Pattlsl H M. Row 

 On Haad 



Partial L1-. 



Soma Canal Groans 



Head and t_L. 

 Canaia DIatlnct 



. Moat Rapid Incraasa In Number* . 



Lana Praaant 

 Eya Functional 



Double Co na«, 

 ONL IMultl-Tlarad 



- Moal Rapid Improvament In Acully - 



Acuity 91' L*ni Rclractor T.L ol Ttcliim Mitotic 8odl«s 

 Maltli on. Appt.t. In ONL 



Only 



Rftlnomolor Rc.pons* (Rods) 



% Responding j 

 To White ^^ 



Seabass so -| 



Predators 



Rapid Improvement 

 I 1 



^^^ 



% Responding ^^ i 



To Anchovy so -j 



Predators 



Slow, Uniform Improvement 



1 . 



14 5 



25 



35 



40 42 



Days At 17-19 'C 



Figure 12. — Developmental events and sensory system development during the early life history of the white seabass. Format is 

 based on Hunter and Coyne (1982). Developmental data are from my study, except some behavioral data from Orhun (unpubl. 

 data) and osteological data from Moser et al. (1983). Y-S = yolk-sac stage, I.O. = infraorbital, S.O. = supraorbital, H.M. = 

 hyomandibular, L.L. = lateralline, T.L. = torus lorigitudinalis, ONL = outer nuclear layer of retina. 



acuity is poor and no acoustic inputs are likely 

 through the swimbladder. During notochord 

 flexion (—5-7 mm SL), visual accommodation is 

 developed with the lens retractor muscle, the 

 swimbladder is inflated (potentially providing 

 acoustic stimuh), and there begins a major re- 

 cruitment of free neuromasts on the head and 

 trunk. Up to this point in development, it would 

 appear that vision plays a limited role in preda- 

 tor detection. 



During the early postflexion stage (~7 mm), 

 the visual system begins to undergo numerous 

 changes (Fig. 12). Acuity continues to improve, 

 early rod precursors develop in the retina, the 

 optic tectum increases markedly in size and 

 stratification, and the torus longitudinalis be- 

 gins to develop in the midbrain. At 10.5-12.5 mm 

 SL, double cones and early rod cells are present 

 in the retina. These changes are essential to 



visual improvement and integration. Visual 

 acuity calculated for most adult marine fishes is 

 2-10 minutes of arc (Tamura 1957); values for 

 adult white seabass are unknown but probably 

 fall in this range. Thus, approximately 75-80% of 

 the improvement in acuity seen from hatch to 

 adult stage in white seabass has occurred by the 

 late larval stage. However, for vision to play a 

 major role in predator detection, improvement 

 in acuity must be accompanied by development 

 of rod cells, by accommodation to distant objects 

 (lens retractor muscle), and by growth and de- 

 velopment of the optic tectum. The development 

 of rod vision helps to improve peripheral vision 

 (O'Connell 1981) and motion detection (Blaxter 

 1986), both crucial aspects of predator detection. 

 Rods also aid in improved visual performance in 

 dimmer light (O'Connell 1981), which would 

 improve foraging skills and predator-detection 



548 



