in plankton samples (Holme 1974). Loligo pealei, 

 however, is commonly collected in the field 

 (Vecchione 1981), but hatches at a much smaller 

 size and is difficult to rear in the laboratory, 

 suffering at least 99'7( mortahty in the first few 

 days, presumably from starvation (Hanlon et al. 

 1987). The former species, therefore, was used 

 for laboratory studies and the latter for field 

 observations, even though extrapolation from 

 one species to another must be approached with 

 caution. 



The L. forbesi hatchlings (< 1 d old) that had 

 not been offered food had unquestionably not 

 fed, but their digestive glands contained many 

 mature cells with conspicuous apical vacuoles. 

 Therefore, the presence or absence of vacuoles is 

 not an adequate indicator of successful first-feed- 

 ing in this species. Even in Sepia, there were 

 indications from tissue-culture experiments that 

 digestive-gland cells may mature slowly in unfed 

 hatchhngs (Boucher-Rodoni et al. 1987). Simil- 

 arly, the large vacuoles cannot be taken as an 

 indication of having fed because the unfed hatch- 

 lings had large vacuoles as did the older L. 

 forbesi that had been fed and had survived for 

 more than 1 week. 



Hatchlings < 1 d old that had been offered food 

 may or may not have fed. However, unfed hatch- 

 hngs typically die, presumably from starvation 

 because the internal yolk sac has been absorbed, 

 within 5 days after hatching. Therefore, the 

 older L. forbesi (>1 wk old) that had been of- 

 fered food probably had fed, although no obser- 

 vations were available to indicate the number of 

 hours or days between their final meal and their 

 time of death and fixation. 



Culturing experiments have indicated that 

 elevated concentrations of DOM enhance sur- 

 vival of paralarval L./br6e.s; (P. G. Lee'). Thus, 

 the squids from the DOM experiment, while not 

 having fed in the typical sense, had grown and, 

 therefore, were not necessarily starving. The 

 DOM added was a complete diet formulation and 

 would have provided all necessary acids. Ap- 

 proximately 50% of the paralarvae in the DOM 

 experiment survived for 10 days after hatching. 

 Ten of 184 paralarvae from the DOM experiment 

 lived for 12 days, before the experiment was 

 terminated because of an intense bacterial bloom 

 (P. G. Lee"). Throughout that period, mortality 

 was higher for paralarvae that had been offered 



food than for those cultured on elevated DOM. 



Digestive-gland structure in the older L. 

 forbesi that had been fed was distinctly different 

 from those raised on DOM. Whereas the fed 

 squids had a few very large vacuoles, the DOM 

 squids had very many smaller vacuoles. As 

 noted above, the large vacuoles cannot be taken 

 as an indication of having fed because the unfed 

 hatchlings also had similarly large vacuoles. 

 Furthermore, digestive-gland tissue was very 

 thin on the fed squids compared with those from 

 either the DOM experiment or the field-collected 

 L. pealei. It is possible that the fed paralarvae 

 had fed enough to survive beyond yolk absorp- 

 tion but not enough to be completely healthy. 



Alternatively, it is possible that the distended 

 lumina and the large vacuoles of the older, fed 

 squids may have been caused by ahmentary fluid 

 reaching the digestive gland and entering the 

 cell by phagocytosis for intracellular digestion. If 

 this was the case, the squids raised on DOM 

 simply would have retained immature digestive 

 gland morphology and histology. However, be- 

 cause the field-collected squids, especially the 

 larger ones, were similar in digestive gland 

 structure to those raised on DOM, it seems hkely 

 that this is the normal, well-nourished condition. 

 Furthermore, the digestive glands of the field- 

 collected squids and those raised on DOM are 

 both similar in structure to the adult condition 

 (c.f. Boucher-Rodoni and Boucaud-Camou, in 

 press). In the largest field-collected squids, 

 which undoubtedly had passed fii'st feeding suc- 

 cessfully, the lumen was largely filled by tissue 

 gi'owth, transforming it into a series of many 

 small tubules. If thin walls of the digestive gland 

 are indicative of poor feeding, none of the field- 

 collected squids showed this indication. 



In conclusion, we are not certain which condi- 

 tion (thin tissue with a few large vacuoles or 

 thicker tissue with many smaller vacuoles) is the 

 healthier state. However, we beheve that it is 

 likely that the condition of thick tissue with 

 many small vacuoles and reduced lumina, found 

 in the DOM and field-collected squids and similar 

 to the adult condition, represents the healthy, 

 well-nourished condition. The differences in 

 gross morphology between these two conditions 

 are obvious even in cursory examination of sec- 

 tions of the digestive glands of paralarvae. This 

 characteristic may therefore be useful for deter- 



'P. G. Lee. University of Texas Marine Biomedical Insti- 

 tute, Galveston. TX, pers. commun. 1986. 



^P. G. Lee, University of Texas Marine Biomedical Insti- 

 tute, Galveston, TX, pers. commun. 1987. 



999 



