KISHKKY BULLhJTlN: VUL. 73, NU. 3 



As a new approach to this problem it is the pur- 

 pose of this study to show how laboratory-spawned 

 fish larvae can be used to detect larval feeding 

 grounds at sea and to point out some of the ways 

 this technique might be used to provide the link 

 between marine food chain research and stock and 

 recruitment predictions in fisheries; the latter by 

 determining what the environmental conditions 

 at sea must be with respect to larval fish food to 

 result in a good or bad survival year for particular 

 species of fish larvae. 



Because it is essential to the general 

 methodology of using larval fishes as assay or- 

 ganisms for the fitness of seawater as larval fish 

 feeding grounds, in the following I describe some 

 background information on maturation and 

 spawning of anchovies in the laboratory; the 

 methods used for feeding larval anchovies; and the 

 laboratory-determined criteria for feeding 

 already known for the larva of this species. A 

 description of the field work is then given, 

 concluding with a discussion of the criteria which 

 can be used to judge the fitness of the larval 

 anchovy's environment. 



THE NORTHERN ANCHOVY 



In the California Current, the major pelagic fish 

 population at present is that of the clupeoid 

 Engraulis mordax, the northern anchovy. This 

 species is found from British Columbia, Canada to 

 Cape San Lucas, Baja California and extending 

 west about 600 km. Although the anchovy has a 

 protracted spawning season from December to 

 August, about three-quarters of its spawning oc- 

 curs in the winter and spring months of January, 

 February, March, and April. The factors affecting 

 larval mortality of clupeoids have been inves- 

 tigated in a number of laboratories throughout the 

 world (Holliday and Blaxter 1963) including my 

 own. Recently, it has been possible to intensify 

 laboratory research at the Southwest Fisheries 

 Center La Jolla Laboratory, National Marine 

 Fisheries Service because of the continuous 

 availability of anchovy larvae. This has been made 

 possible by inducing sexual maturation of adults 

 in the laboratory resulting in daily spawning and 

 fertilization of anchovy eggs throughout the year. 

 Details of this maturation and spawning tech- 

 nique are given by Leong (1971) and Lasker (in 

 press). The availability of first-feeding larvae 

 hatched from laboratory-spawned eggs has made 

 possible the development of a technique whereby 



specific areas of the ocean could be examined for 

 their potential as larval feeding grounds, and 

 criteria established to characterize parts of the 

 ocean as good or bad areas for larval survival. 



LABORATORY-DETERMINED 



CRITERL\ FOR SUCCESSFUL 



LARVAL ANCHOVY FEEDING 



A background of information on larval anchovy 

 feeding is available from a number of studies and 

 was used to guide this investigation. 



1. Particle size at first feeding appears to be crit- 

 ical. First-feeding anchovy larvae (standard 

 length 3.5 mm) have small mouths and require a 

 food particle about 50 ]u.m in diameter, although 

 particles larger than 100 /j,m may be taken (Berner 

 1959). Smaller particles may not be visible to the 

 larvae. Berner (1959) reported that anchovy larvae 

 smaller than 4 mm long taken in plankton tows 

 had eaten particles ranging in length from 24 to 

 186 /xm. However, over 70% of the food in their 

 intestines was between 60 and SOjxm long. 



2. The number of particles per unit volume in the 

 anchovy larva's environment must be above a 

 minimum concentration. O'Connell and Raymond 

 (1970), using natural plankton as food, showed that 

 the survival of first-feeding anchovy larvae was 

 dependent, in their experiments, on the number of 

 micronauplii per unit volume available to the lar- 

 vae. Successful first feeding, as pointed out by 

 Hunter (1972), also depends on a sufficiently high 

 density of food particles to compensate for the low 

 capture efficiency (about 10%) exhibited by 

 anchovy larvae when they begin to feed. 



3. The kind of food organism determines survival 

 and growth. Lasker et al. (1970) fed a variety of 

 phytoplankters and zooplankters to first-feeding 

 anchovy larvae. Only one phytoplankter of those 

 tested, Gymnodinium splendens, supported 

 growth and gave relatively good results in survival 

 experiments when compared with larvae fed nat- 

 ural plankton. The rotifer Brachionus plicatilis, 

 although not found in the anchovy's normal habi- 

 tat, also could be used as a laboratory food for older 

 anchovy larvae and a small proportion of first- 

 feeding larvae (Theilacker and McMaster 1971; 

 Hunter 1972). 



4. The greater the concentration of food particles, 

 the more frequent are the feeding strikes made by 

 anchovy larvae; consequently the greater the suc- 

 cess in capturing food. Although examination of 

 field-caught anchovy larvae reveal very few with 



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