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



shrinkage due to time-in-net and preservation 

 (Theilacker 1980)) and the height of the midgut 

 cells. The adjusted SL and absolute midgut cell 

 height classifies each larva into a size, diet, and 

 midgut cell height category. The numbers of 

 larvae belonging to each category are divided by 

 the category durations to yield the number of 

 larvae per day per category. To estimate the 

 percentage of larvae dying per day due to star- 

 vation, the starved category is divided by the 

 total number. An example of these manipula- 

 tions in Table 5 (taken from Owen 1989; this 

 issue) shows that mortaUty due to starvation 

 was estimated to be 24%/d for first-feeding an- 

 chovy larvae collected off southern California. 



(taken on sagittal sections that were prepared 

 for histological examination) defines past feeding 

 history. Kostomarova (1962) also measured the 

 height of intestinal cells of larval fishes to evalu- 

 ate their state of health. Although she found a 

 relation between fish condition and size of mid- 

 gut cells, the relation was not quantified. In our 

 study, we estabhsh criteria for discriminating 

 the condition of laboratory-raised larvae using 

 the midgut cell height and for estimating rates of 

 starvation in the field. 



To validate this technique, it was necessary to 

 measure the effects on the midgut cells of the 

 prolonged processing periods, commonly en- 

 countered at sea. The elapsed time for standard 



Table 5. — Histological condition of larval northern anchovy off 

 southern California. (From Owen et al. 1989: table 7.) 



'Number of fieW-collected larvae belonging to each size, diet, and 

 midgut-cell-height category 



^Response times for eacti size, diet, and midgut-cell-tieight category 

 (see text) 



'Number/duration = No./d. 



To complete these manipulations for the next 

 size class, 4-<5 mm, fed and intermediate 

 larvae were discriminated using the same cell 

 height measurement, 17.5 \x.m, and starved lar- 

 vae did not grow into this size class (Table 3). 

 The duration for the fed category was 2.5 days 

 and for the intermediate category averaged 3 

 days. The 2.5 d duration for the fed category was 

 obtained by dividing the size-class interval by 

 the growth rate, 0.41 mm/d. Larvae from the 

 delayed-feeding treatments that belonged to the 

 intermediate category outgrew this size class 

 within 2-4 days (Table 1). Some larvae belong- 

 ing to the group where feeding was delayed 1 

 day (Sl/F) had recovered and entered the fed 

 category by the time they grew to 4.00 mm. 



Cell heights cannot be measured for northern 

 anchovy larger than 6 mm SL as the midgut 

 folds, increasing the absorptive area and making 

 cell heights difficult to measure. 



DISCUSSION 



The height of northern anchovy midgut cells 

 466 



ichthyoplankton net hauls to 225 m is 21 minutes, 

 and additional time is needed for washing down 

 the net and for sample preservation (Smith and 

 Richardson 1977). To quantify the effect of col- 

 lecting time and processing time on autolysis, we 

 simulated the net collection and used a matrix of 

 8 time periods, ranging from to 25 minutes, 

 followed by preservation in either of two fixa- 

 tives, Bouin's or formahn. Initially, alcohol also 

 was tested because we anticipated using the 

 same fish to study both gi'owth and condition. 

 (80% alcohol is routinely used to preserve 

 otoliths.) Unfortunately, we found alcohol use- 

 less for histopathology. 



The height of the midgut cells did not change 

 over the 25 m net treatment, but the standard 

 length decreased. Thus, for field collections, it is 

 not necessary to adjust midgut height for time- 

 in-net, but it is important to correct standard 

 length of field-collected larvae for shrinkage in 

 order to allocate the larvae into the correct 

 length categories. The model (Theilacker 1980) 

 used to adjust length was generated for for- 

 malin-preserved anchovy. Perhaps the slight 



