EFFECT OF TEMPERATURE ACCLIMATION ON GOLDFISH {CARASSIUS AURATUS) INTESTINAL TRANSPORT J. A. Groot, H. Albus, R. Bakker, J. Siegenbeek van Heukelom and M. M. A. Suykerbuijk Department of Animal Physiology, University of Amsterdam, Kruislaan 320,1098 SM Amsterdam, The Netherlands

Oxygen consumption of goldfish acclimated to different temperatures increases more than five times as the acclimation temperature is raised from 10° to 30° (1). Smith (2) concluded that the amino acids, transported by the goldfish intestine, may be devided in two groups; a group that shows compensation and a group of which the final concentration in the sacs was not influenced by acclimation temperature. This group is named "non adapting" amino acids. No data on the influence of tempe­rature acclimation on sugar transport are available. However, if the glucose evoked potential, measured by Smith is indicative for the difference between cold and warm acclimated fish then one should expect a reduction of sugar transport upon warm acclimation. This is not in agreement with the metabolic need. However an uncoup­ling of electrical phenomena and sugar transport at high acclimation temperature may occur by modification to the carrier mediated entry of sugars through the intestinal wall (2). Experiments were performed with animals obtained through local dealers from Italy and Japan. The fish were kept for at least 6 months in aereated tanks under a 12 h light:12 h darkness photoperiod regime. Temperature acclimation was at 10° and 30° for at least 4 weeks. Fish at 30° were continuously fed with Tetramin, the other fish once a day. In table 1 the results of measurements on everted sacs are presen­ted. The 3-OMG flux in sacs from 30° fish, normalised to wet weight is significant­ly higher than that in sacs from cold acclimated fish at 30°. In table 2 results of unidirectional flux measurements at 30° with mucosal epithelium stripped free from underlying muscular layer (3) and the influence of phlorizin are combined. The phlorizin-sensitive flux, as well as the phlorizin-insensitive flux in strips of warm acclimated fish are again greater than in strips from cold fish. If fluxes are calculated per unit of area the difference is not significant. The weight of intestinal tissue of warm acclimated fish is again less than that of cold fish.

Table 1. Water transport and netto 3-OMG flux in everted intestinal sacs. Initially 7 mM 3-OMG at both sides. Incubation time 90 minutes.

Accl. temp.

10°

30°

wet weight mg

124+5 (57)

93+4 (42)

Incubation temp. 10° 20° 30° water : yl/mg.h 3-OMG :nmo1/mg.h

water : pl/mg.h 3-OMG :nmo1/mg.h

0.04 +_ 0.01(9) 1.7 +_ 0.3

0.03 +_ 0.01(5) 1.8 +_ 0.2

0.09 +_ 0.02(11) 3.0 +_0.5

0.14 +_ 0.02(9) 3.6 +_0.5

0.20 + 0.03(17) 4.4 +_ 0.5

0.35 ± 0.05(12) 8.0 + 1.0

117

118 J. A. Groot et at.

Table 2. Ace1.temp.

wet weight of 0.2 cm strip

Unidirectional 3-OMG flux from mucosa to serosa in nmol/mg.h calculated from 15 min.samples.

- phlorizin + phlorizin 10 M. 10° 30°

6.17 + 0.43 (21) 3.52 + 0.46 (14)

26,1 + 2.4 (63) 56.9 + 7.6 (39)

8.3 + 1.6 (39) 20.6 + 5.8 (26)

Results of electrical measurements at 10°, 20°and 30° on perfused intestinal seg­ments (4) are presented in fig.l. At all temperatures and in all segments of cold and warm acclimated fish the transmural potential difference increased upon addi­tion of glucose to the mucosal perfusion solution (Glucose Evoked Potential). The glucose induced current in 10 acclimated fish is greater than in warm acclimated fish.

Figure 1 Glucose evoked potential Transaural resistance

ace1.temp. 10°

Glucose induced current

■150 PA

Electrical measurements in stripped mucosa confirmed that the resistance of intes­tine of warm fish is lower than that from cold acclimated fish. To compare the glu­cose induced current in cold and warm acclimated fish it is necessary to have an estimate of the mucosal area that generates this current. Preliminary measurements of the electrical capacity of mucosal strips suggest that the ratio of mucosal to serosal area in warm acclimated fish is reduced. This is fully in accord with his-tological examinations.

In summary: the sugar transport through intestinal preparations from cold and warm acclimated fish shows no compensation in the sense that the net flux in warm acclimated fish is lower than that from cold acclimated fish measured at the high acclimation temperature and therefore resembles the "non adapting" amino acids. Although the GEP in warm acclimated fish is much lower than in cold acclimated fish, preliminary experiments suggest that there is also a decrease in mucosal area. At the moment no conclusion can be drawn whether temperature acclimation modifies the sodium dependent sugar transport system.

1. Fry, F.E.J., and P.W. Hochachka (1970) In G.Causey Whittow (Ed.) Comparative Physiology of Thermoregulation. Academic Press New York. pp.79-134.

2. Smith M.W. (1976). Biochem.Soc.Symp. 41, 43-60 3. Groot, J.A., H.Albus, J.Siegenbeek van Heukelom (1979).Pfliigers Arch. 379,1-9. 4. Albus, H and J. Siegenbeek van Heukelom (1976). Comp.Biochem.Physiol. 54A.

113-119.