THEILACKER: EFFECT OF STARVATION ON JACK MACKEREL 



1.66 (the break points establish three equal 

 groups). 



Data Analysis 



In the main, conclusions are based on the results 

 of a stepwise discriminant analysis (SWDA). A 

 discriminant analysis allows one to distinguish 

 between two or more groups, given a set of vari- 

 ables that describe the characteristics in which 

 the individuals in each group are expected to dif- 

 fer. In the stepwise discriminant analysis, all the 

 variables are introduced into a SWDA computer 

 program and the best set of variables, based on the 

 generalized Mahalanobis distance (Rao 1952), is 

 selected. The first variable chosen will usually be 

 the one which gives the best score when classify- 

 ing the individuals into their predetermined 

 groups. The score is equal to the number correctly 

 classified. The selection of each succeeding vari- 

 able improves the score until a subset is chosen 

 which is as good as the full set of variables for 

 discriminating the groups. All variables not in- 

 cluded in the final subset are considered superflu- 

 ous, or not necessary for classification. 



RESULTS 



between the round cells. In starved larvae, mitotic 

 activity was arrested and many of the cells were 

 shrunken, which caused large clear areas to ap- 

 pear between densely stained, atrophied cells. 



Liver (Figures 5-8) 



In the normal larval jack mackerel liver the 

 hepatic cords were two cells thick. Within each 

 hepatocyte, the nucleus (3) was regular in shape 

 and distinct. The cytoplasm (4) was well dispersed 

 with intracellular spaces, probably an area where 

 glycogen and lipid are stored. Sinusoid areas, 

 where metabolic exchanges take place between 

 the hepatic cords, contained blood cells. After 

 starvation for a few days, the liver atrophied, the 

 cytoplasm condensed, stained darkly, and in- 

 tracellular spaces had disappeared. There were 

 focal degenerative or necrotic areas and accumu- 

 lations of eosinophilic granules and masses. Nuc- 

 lei were often irregular in shape and granules 

 appeared around their periphery; these darkened 

 areas are presumed to be condensed, inactive 

 chromatin (Stein et al. 1975). The gallbladder (5) 

 in starved larvae was always enlarged; normally 

 it discharges its contents under the stimulus of 

 food (Love 1970). 



Histological 



The histological condition of yolk-sac and ac- 

 tively feeding larvae ("normal") was compared 

 with that of 3-day starved larvae and many differ- 

 ences were noted in the cells, tissues, and organs. 

 The degree of apparent histological deterioration 

 of 1- and 2-day starved larvae was intermediate 

 between the "normal" and moribund status. This 

 condition was termed "semi-starved" by Umeda 

 and Ochiai (1975) and "intermediate" by O'Con- 

 nell(1976). 



The following section describes the normal his- 

 tology of actively feedingjack mackerel larvae and 

 that of starving larvae. Twelve histological 

 criteria, which appeared to be indicators of starva- 

 tion, were identified; they are numbered in the test 

 below and are referenced in the photomicrographs 

 (Figures 1-12). 



Brain (Figures 3, 4) 



The primitive brain cells exhibited a high inci- 

 dence of mitotic activity (1) in normal larvae and 

 there was relatively little intercellular space (2) 



Pancreas (Figures 5-8) 



Cells of the exocrine pancreas were arranged in 

 series, in a circular fashion, as a secretory unit 

 called an acinus. The nucleus (6), clear and dis- 

 tinct, was located in the basal portion of the 

 pyramidal cells. The acinar arrangement of the 

 pancreatic cells (7) was found to be very sensitive 

 to deprivation of food. A breakdown in the sym- 

 metry in the acinus was slight but usually detect- 

 able after 1 day of starvation. Tissue degeneration 

 after 3 days of starvation was extreme. The nu- 

 cleus was irregular and uniformly stained and 

 there was no detectable acinar arrangement. The 

 presence of zymogen, digestive proenzyme se- 

 creted by the acinus and stored as granules at its 

 central apex, was usually associated with starva- 

 tion. 



Digestive Tract (Figures 7-12) 



The columnar epithelial cells of the midgut were 

 closely united (8) in a single layer. Microvilli were 

 visible along the border of the lumen giving a 

 brush effect. In starved larvae, the midgut cells 



405 



