ecology. Histology has been used to determine 

 whether larval fishes are starving at sea 

 (O'Connell 1976, 1980; Theilacker 1978, 1986; 

 Govoni 1980; Eldridge et al. 1981; Kashuba and 

 Matthevi^s 1984). In cephalopods, the digestive 

 gland is uniquely suited to be a target for a his- 

 tological study of feeding history. The cells of the 

 digestive gland can be categorized along a de- 

 velopmental continuum of immature, synthesiz- 

 ing, mature, and resting cells of a single type 

 (Boucaud-Camou and Yim 1980; Boucaud-Camou 

 and Boucher-Rodoni 1983; Boucher-Rodoni et al. 

 1987). Boucher-Rodoni et al. (1987) proposed 

 that the developmental condition of the cells of 

 the digestive glands of very young Sepia offi- 

 cinalis and other cephalopod paralarvae could be 

 used as an indicator of successful first-feeding. 



The digestive-gland cells in the genus Loligo 

 undergo a developmental sequence similar to 

 that of other cephalopods (Portmann and Bidder 

 1928), although Boucher-Rodoni and Boucaud- 

 Camou (in press) have found that the digestive 

 gland in Loligo differs substantially from that of 

 other cephalopods. The cells of the loliginid di- 

 gestive gland are characterized by large apical 

 vacuoles containing lipids and carbohydrates 

 (Bidder 1950, 1966). 



We examined the digestive glands of para- 

 larval Loligo, both L. pealei from field collec- 

 tions and L. forbesi that had been hatched and 

 maintained in the laboratory under known nu- 

 tritional conditions. Specifically, we wanted to 

 see whether the presence of mature digestive- 

 gland cells could be associated with successful 

 first-feeding in the commercially important 

 squid family Loliginidae. 



Materials and Methods 



Laboratory squids were obtained from an ex- 

 periment in culturing the eastern Atlantic 

 species Loligo forbesi (Hanlon et al. 1985). Be- 

 cause the primary objective of the experiment 

 was to determine methods for successfully cul- 

 turing squids, the squids could not be sacrificed 

 on an optimum schedule for determination of 

 starvation. Furthermore, because the scope of 

 the feeding experiments was Hmited, the sample 

 available to us (other investigators were inter- 

 ested in other problems) was quite small. 



These squids included hatchlings (<1 d old), 

 some of which had been offered zooplankton as 

 food and some that had been kept without food. 

 Also included were squids >1 wk old. These 

 older squids had survived past the point at which 



death from starvation normally occurs in unfed 

 squids. Among these older squids were some 

 that had been offered zooplankton as food and 

 some that had been kept without food in a sea- 

 water culture medium containing a high concen- 

 tration (10 mg C per L) of dissolved organic 

 material (DOM). Squids collected in the field 

 were Loligo pealei sorted from zooplankton 

 samples from the western North Atlantic. The 

 L. pealei were chosen to represent the entire 

 paralarval size range (Vecchione 1981) (Table 1). 



Table 1 . — Paralarval squids examined for digestive-gland 

 histology. DOM = Dissolved Organic Material. 



The field-collected squids were fixed and pre- 

 served in 4% formaldehyde in seawater, whereas 

 those cultured in the laboratory were fixed in 

 Bouin's solution and sectioned shortly after fixa- 

 tion. For all squids, 10 |xm horizontal sections 

 were prepared after having been embedded in 

 paraffin. Sections were cleared with oil of 

 wintergi-een and stained with hematoxylin and 

 eosin. Observations were standardized by select- 

 ing sections that, as much as possible, were ven- 

 tral to the posterior salivary gland and dorsal to 

 the ink sac, although in some squids these organs 

 overlapped dorsoventrally. 



Results 



Some mature cells containing conspicuous 

 apical vacuoles were found in all squids. Num- 

 bers and sizes of vacoules varied as did the rela- 

 tive volume of the glandular epithehum of the 

 digestive gland. 



Hatchlings of L. forbesi were all similar in 

 appearance, both nonfed (Fig. lA) and those 

 that had been offered food and therefore may 

 have fed (Fig. IB, C). The digestive glands ap- 

 peared to be robust, with thick glandular epi- 

 thelium that occupied more volume than the 



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