de VLAMING: CONTROL OF FATTENING IN NOTEMIGONUS 



exposed to a warm temperature. For example, 

 lipid levels were not significantly different in 

 pinealectomized fish exposed to the short pho- 

 toperiod-warm temperature regime and sham 

 operated animals maintained on the long pho- 

 toperiod-warm temperature regime; nor was fat 

 "content significantly different in sham operated 

 animals exposed to the short photoperiod-warm 

 temperature condition and pinealectomized fish 

 maintained on the long photoperiod-warm 

 temperature regime (Tables 2, 3). 



In all three of the experiments summarized 

 here, body fat reserves were significantly greater 

 in pinealectomized than in sham operated females 

 maintained on the long photoperiod-low tempera- 

 ture regime; similar results were recorded in two 

 of the experiments with males. Body fat composi- 

 tion was significantly lower in pinealectomized 

 than in sham operated females exposed to a short 

 photoperiod-low temperature regime; similar 

 differences were noted with males in two of the 

 experiments. These data further confirm the 

 suggestion that the effects of pinealectomy on 

 Hpid metabolism in Notemigonus depend on pho- 

 toperiod. In two of the experiments, fat content 

 did not differ significantly in pinealectomized fish 

 maintained on the long photoperiod-low tempera- 

 ture regime and sham operated animals exposed to 

 the short photoperiod-low temperature regime; 

 nor were significant differences noted in fat levels 

 when the reverse comparison was made (Tables 2, 



3). 



The data obtained at both high and low 

 temperatures indicate that the pineal in 

 Notemigonus may have some role in receiving 

 and/or integrating light information. Such a 

 suggestion seems likely since the pineal may 

 either facilitate or retard lipid deposition in this 

 species. Several morphological and elec- 

 trophysiological studies suggest that the pineal in 

 some teleosts functions as a photoreceptor (cf. de 

 Vlaming 1974). Light microscope studies on the 

 pineal of Notemigonus also indicate a sensory 

 function (Vodicnik and de Vlaming unpubl. data). 

 If the pineal in Notemigonus is a photoreceptor 

 involved by some means in measuring daylength, 

 then removal of this organ from fish maintained 

 under different photoregimes might be expected 

 to have variable effects on lipid metabolism. 

 Urasaki (1972a, b) has also shown that the effects 

 of pinealectomy on reproductive function in 

 Oryzias latipes vary with photoperiod conditions. 



The effects of the pineal on lipid metabolism in 



Notemigonus, however, do not depend entirely on 

 light information. For example, in fish maintained 

 on a long photoperiod during the prespawning and 

 spawning seasons, pinealectomy accentuated lipid 

 deposition at low temperatures and lipid depletion 

 at a high temperature. Temperature may not, 

 however, act on the pineal directly. High 

 temperatures cause lipid catabolism and low 

 temperatures favor lipid deposition. Temperature 

 may act directly on lipid metabolism enzyme sys- 

 tems or indirectly to stimulate hormone secretion 

 from various endocrine glands. In Notemigonus, 

 light information serves only to modify the effects 

 of temperature on lipid metabolism. Thus, the 

 pineal could function at all temperatures as a light 

 receptor and/or integrator. Light information 

 may be differentially interpreted (at different 

 temperatures or at different times of the year) at 

 some other level such as the hypothalamus and/or 

 pituitary. 



Whether the pineal in Notemigonus exerts its 

 effects on lipid metabolism via neural or hormonal 

 pathways is not presently known. Most 

 morphological studies on the teleost pineal have 

 stressed the dual sensory and secretory ap- 

 pearance of this organ (cf. de Vlaming 1974). A 

 dual sensory-secretory function is also indicated 

 by light microscope studies on the pineal of 

 Notemigonus. Histochemical and biochemical data 

 show that the teleost pineal has an active in- 

 dolamine metabolism (Quay 1965; Hafeez and 

 Quay 1969; Fenwick 1970; Owman and Riideberg 

 1970). Melatonin has inhibitory effects on 

 reproductive function in various teleosts (Fenwick 

 1970; Urasaki 1972c; de Vlaming, Sage, and Charl- 

 ton 1974). Melatonin treatment decreases lipid 

 reserves in F. similis maintained on a long pho- 

 toperiod-low temperature regime (de Vlaming, 

 Sage, Charlton, and Tiegs 1974); if melatonin acts 

 as the mediator of pineal action in Notemigonus, 

 one might then expect pinealectomy to increase 

 fat levels in fish exposed to a long photoperiod-low 

 temperature regime. Pinealectomy did indeed 

 have these results under this regime. During July, 

 melatonin therapy of F. similis exposed to a short 

 photoperiod-low temperature regime stimulated 

 lipid deposition (de Vlaming, Sage, Charlton, and 

 Tiegs 1974). If the mediator of pineal activity in 

 Notemigonus is melatonin, one might predict that 

 pinealectomy would decrease body lipid stores in 

 animals exposed to a short photoperiod-low 

 temperature regime. Such results were observed 

 in the experiments reported here. Interestingly, 



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