THEILACKER: CHANGES IN BODY MEASUREMENTS OF LARVAL NORTHERN ANCHOVY 



ences between treatments (live, net treated, and 

 preserved) were significant (P<0.01). Even though 

 these differences were significant, the small 

 changes in eye diameter size caused by net treat- 

 ing and preserving probably are not important for 

 calibration of size of field-collected larvae. Thus 

 eye diameter should be a useful parameter for 

 estimating average live standard length of field- 

 collected larvae (Table 1). 



DISCUSSION AND CONCLUSION 



The causes of antemortem shrinkage offish lar- 

 vae are not completely understood. Before death, 

 appearance of the body changes from translucent 

 to opaque. This phenomenon is an indicator of 

 ensuing death of larvae in rearing experiments. 

 Autolysis, digestion of tissues by their own en- 

 zymes, is occurring during this antemortem 

 period (Theilacker 1978 ), and the enzymatic action 

 on proteins may cause denaturation, thus the color 

 change and shrinkage. Shrinkage also may be 

 caused by an osmoregulatory problem. An inabil- 

 ity to osmoregulate may develop from loss of 

 mucus by abrasion after contact with a surface. 

 The internal osmolar concentration of another 

 clupeoid larva, Pacific sardine, Sardmops sagax, is 

 0.24 M and that of seawater 0.56 M (Lasker and 

 Theilacker 1962). If a larva were unable to os- 

 moregulate, this difference in osmolarity would 

 cause it to lose fluid and shrink. 



The amount of shrinkage that occurred before 

 larvae were killed in a preservative was depen- 

 dent on larval fish size and the extent of "han- 

 dling" (measuring and netting). The elapsed time 

 of surface contact was the main determinant of 

 final length. This was especially noticeable while 

 measuring small, 3-7 mm larvae. As larvae in- 

 creased in size and ossification progressed, net- 

 treatment shrinkage decreased. 



Preserving larvae after handling caused addi- 

 tional shrinkage that was a constant proportion of 

 size. Laboratory-preserved shrinkage in Formalin 

 included a 30 s handling time; shrinkage in For- 

 malin was constant at 8'7c and independent of size. 

 Preserving larvae that had been retained in a net 

 caused an additional 37^ shrinkage; the additional 

 shrinkage was nearly a constant proportion of 

 size. 



Farris' (1963) results on shrinkage of labora- 

 tory-preserved, 3-6 mm yolk-sac Pacific sardine 

 larvae agree with my results. He found Formalin 

 shrinkage of standard length ranged between 7 



and 11'%^, similar to the 8*7^ shrinkage for 

 laboratory-preserved northern anchovy in my 

 study. Rosenthal et al. (1978) reported a I67c 

 shrinkage of newly hatched, 2 mm larvae of the 

 sea bream, Chrysophrys major. The larvae were 

 anesthesized with MS-222 and measured with a 

 projector prior to preservation in Formalin. It ap- 

 pears that handling of the sea bream was minimal; 

 however, MS-222 has been reported to interfere 

 with osmoregulation (Parker 1963), and an inabil- 

 ity to osmoregulate would cause a greater shrink- 

 age. Blaxter (1971) reported on a net-shrinkage 

 experiment that was similar to my study. After his 

 net treatment, mean live size of 22 herring larvae 

 (10.77 mm) decreased by 17'7f ; Formalin fixation 

 caused an additional 3-5*%^ shrinkage for a total of 

 20-22^f . He noted the larvae were dead after net- 

 ting, but the elapsed time is unknown. In this 

 study, the netted 11 mm northern anchovy were 

 usually dead after 20 min, and the total shrinkage 

 of the 20-min treated 11 mm northern anchovy 

 was about 18*%^, similar to Blaxter 's experiment. 



If the larvae to be measured are badly damaged 

 or partially digested, the models generated in this 

 study, which describe live body proportions and 

 shrinkage, could be used to estimate average fish 

 length from size of head or eye. Packard and 

 Wainwright (1974) found that eye diameter of 

 young herring (up to 100 mm) was a useful refer- 

 ence parameter for estimating both size and 

 weight. Because eye diameter of northern anchovy 

 changed little during netting and preservation, 

 eye diameter may be a useful parameter for es- 

 timating average live size of field-collected larvae. 

 However, use of eye diameter to estimate live stan- 

 dard length assumes that the relation between eye 

 diameter and standard length is the same for 

 laboratory-reared and field-collected larvae. Bal- 

 bontin et al. ( 1973) and Blaxter ( 1976) have shown 

 that morphological differences exist between 

 reared and wild fish of the same length, thus the 

 assumption, that the body forms of reared and wild 

 northern anchovy larvae are similar, may be in- 

 valid. However, as I have shown in this study, the 

 method of handling larvae prior to preservation 

 causes shrinkage differences that could be inter- 

 preted as morphological differences. 



The most important use of the shrinkage models 

 is to predict live size, and thus age, of sea-collected 

 northern anchovy larvae so that results from 

 laboratory larval fish studies can be related to the 

 sea. Use of the standard length shrinkage model 

 (Table 4) should give the best estimate of live size 



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