CHANGES IN BODY MEASUREMENTS OF LARVAL 



NORTHERN ANCHOVY, ENGRAULIS MORDAX, AND OTHER FISHES 



DUE TO HANDLING AND PRESERVATION 



Gail H. Theilacker* 



ABSTRACT 



The relation between northern anchovy length and body parts was compared for live and laboratory- 

 preserved larvae as well as larvae treated in a net to simulate field collection conditions. Larvae were 

 damaged by net abrasion, and those netted before preservation shrank more than those that were 

 laboratory preserved (that is, larvae pipetted directly into preservative). Shrinkage of net-treated 

 individuals decreased with age and increased with handling time, but shrinkage of laboratory- 

 preserved larvae was constant for the size class studied. The results show that morphological differ- 

 ences reported for laboratorv'-reared and sea-caught larvae of the same length may result from the 

 method of handling larvae prior to preservation. 



To describe life stages of larval fish, field and 

 laboratory studies rely on length measurements of 

 preserved sea-collected and preserved labora- 

 tory-collected larvae. Sea-collected larvae incur 

 mechanical damage, abrasion from the collecting 

 net and from other plankters, while the net is 

 being towed and washed down (Ahlstrom 1976). 

 When damaged, delicate larvae shrink. This ini- 

 tial shrinkage usually occurs before death, and 

 this shrinkage is compounded by preservative 

 shrinkage (Blaxter 1971). Conversely, laboratory 

 handling of larvae prior to preservation is less 

 damaging than net abrasion. In the laboratory, 

 individual larvae are usually transferred by 

 pipette or beaker to preservative, and they die and 

 shrink in the preservative. 



Laboratory-reared fish larvae differ morpholog- 

 ically from sea-caught larvae. Body depth of wild 

 herring, Clupea harengus, larvae was smaller 

 than that of starved laboratory-reared larvae of 

 the same preserved length (Blaxter 1971). Ryland 

 (1966) observed that sea-sampled larval plaice, 

 Pleuronectes platessa, were smaller than labora- 

 tory larvae at a comparable stage and suggested 

 that a factor for shrinkage was needed to equate 

 field with laboratory measurements. I have 

 noticed a similar discrepancy in preserved length 

 of sea-collected yolk-sac larvae and laboratory- 

 hatched and preserved yolk-sac larvae of the jack 

 mackerel, Trachurus symmetricus (Theilacker 



'Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 

 92038. 



Manuscript accepted January 1980. 

 FISHERY BULLETIN: VOL' 78. NO. .3. 1980. 



unpubl. data). These morphological differences 

 may be the result of the method of handling 

 (laboratory capture or net capture) prior to pres- 

 ervation. Since it is necessary to compare animals 

 at the same developmental stage to relate labora- 

 tory larval fish studies to the field, there is a need to 

 intercalibrate field (preserved) and laboratory 

 (live and preserved) larval fish measurements. 



METHODS 



Adult northern anchovy, Engraulis mordax, 

 maintained in the Southwest Fisheries Center's 

 aquarium, were spawned by hormone injection 

 (Leong 1971). I reared the anchovy larvae at 15.5° 

 C on cultured food organisms {Gymnodinium 

 splendens; rotifers, Brachionus plicatilis; and 

 copepods, Tisbe furcata) in 100 1 tanks using 

 methods described by Lasker et al. (1970), 

 Theilacker and McMaster (1971), and Hunter 

 (1976). 



I considered several factors that could affect 

 shrinkage of larval fish: 1) size, 2) type of fixative, 

 3) treatment of larvae before fixation (net or 

 laboratory capture), and 4) duration of net reten- 

 tion. Larval fish measurements fit into four treat- 

 ment categories (Figure 1): 1) live, 2) laboratory 

 pipetted and preserved, 3) net treated, and 4) 

 preserved after net treatment (equivalent to 

 "field-collected" larvae). Five body measurements 

 (in millimeters) were taken: standard length (SL), 

 tip of upper jaw to perpendicular at end of 

 notochord; head length, tip of upper jaw to clei- 

 thrum; body depth at the pectoral (not measured 



685 



