de VLAMING: CONTROL OF FATTENING IN NOTEMIGONUS 



exposed to the long photoperiod, body lipid levels 

 in pinealectomized fish were significantly lower. 

 Gonadal regression was also initiated in sham 

 operated fish maintained on the 9L/15D-25°C 

 regime; spawning was observed in pinealec- 

 tomized animals on this regime. Body lipid levels 

 were significantly greater in pinealectomized fish 

 than in sham operated fish maintained on the 

 short photoperiod-warm temperature regime. In 

 animals maintained at a low temperature (both 

 photoperiods), GSIs did not differ significantly in 

 the pinealectomized and sham operated groups. 

 Sham operated fish, however, were significantly 

 fatter than the pinealectomized animals 

 experiencing the 9L/15D-15°C regime. Further- 

 more, under the 15.5L/8.5D-15°C regime, 

 pinealectomized fish contained significantly more 

 fat than the sham operated controls. 



DISCUSSION 



Both temperature and photoperiod have a dis- 

 tinct effect on body lipid reserves in N. 

 crysoleucas. During the prespawning and spawn- 

 ing seasons, low temperature treatment (12°- 

 15°C) favors increases in body fat stores in both 

 sexes of Noteniigonus, regardless of photoperiod 

 conditions. Low temperature treatment of 

 Noteniigonus during the gonadal preparatory 

 season did not result in lipid deposition, but did 

 maintain body fat composition at a level 

 equivalent to that in the initial controls (sacrificed 

 at the onset of the experiment). Animals collected 

 during the preparatory period (January) were 

 very fat. In fact, body fat stores in this species 

 reach a peak in late December, January, and early 

 February. The failure of laboratory low tempera- 

 ture treatment to stimulate lipid deposition dur- 

 ing the preparatory season could be due to the 

 presence of sufficient fat reserves in the initial 

 controls. Regardless of season or photoperiod, high 

 temperature (25°C) acclimation favors body lipid 

 depletion in males. During the preparatory and 

 prespawning seasons, body fat depletion is also 

 observed in females exposed to warm tempera- 

 tures. Compared to initial controls (animals 

 sacrificed at the beginning of the experiment), 

 lipid levels in Noteniigonus maintained at warm 

 temperatures during the early spawning season 

 were not appreciably altered. The failure of warm 

 temperature treatment to deplete lipid reserves in 

 females during the early spawning season may be 



due to the relatively low levels of fat in the initial 

 controls. Fish maintained at warm temperatures 

 were fed twice daily whereas fish exposed to low 

 temperatures were fed only once a day; warm 

 temperature animals consumed four to five times 

 more food than the low temperature fish. Since the 

 fish in all experiments were fed ad libitum, the 

 differences in body lipid levels should not be due 

 entirely to higher metabolic rates at elevated 

 temperatures. Lipid synthesis and deposition is 

 also promoted at low temperatures in several other 

 teleost species (Blazka 1958; Brown 1960; Dean and 

 Goodnight 1964; Knipprath and Mead 1968; de 

 Vlaming and Pardo 1975). The means by which 

 temperature acts to control lipid metabolism is not 

 fully understood, but Kinne (1960) reported that 

 the efficiency of food conversion in Cyprinodon 

 macularis is maximal at lower temperatures. 

 Furthermore, enzyme systems (Hochachka 1969) 

 and hormones (de Vlaming and Pardo 1975; Pardo 

 and de Vlaming in press) involved in lipid me- 

 tabolism in fishes appear to be temperature sensi- 

 tive. 



At low temperatures, short photoperiods are 

 more effective than long photoperiods at 

 stimulating lipid deposition in Noteniigonus. In all 

 of the experiments reported here, body lipid 

 reserves were higher in female fish exposed to the 

 short photoperiod-low temperature regimes than 

 in females maintained on long photoperiod-low 

 temperature regimes. With the exception of the 

 experiment conducted during the prespawning 

 season, similar results were obtained with males. 

 Short photoperiods also compliment the lipid 

 depleting effects of warm temperatures. In two of 

 the three experiments summarized here, body fat 

 reserves were significantly lower in fish (both 

 sexes) exposed to the short photoperiod-warm 

 temperature regime than in animals maintained 

 on the long photoperiod-warm temperature 

 regime. Thus, in Noteniigonus, the effects of pho- 

 toperiod on lipid metabolism are temperature 

 dependent. Specifically, in combination with a low 

 temperature, short photoperiods favor body fat 

 deposition, but at a high temperature, short pho- 

 toperiods accelerate depletion of lipid reserves. 

 The fact that short photoperiods have opposing 

 effects on lipid metabolism depending on 

 temperature is, at the present time, an enigma. 

 Apparently, however, changing environmental 

 temperatures can differentially sensitize 

 Noteniigonus to daylength. Roberts (1964) showed 

 that photoperiod changes can alter metabolic pat- 



771 



