I have been keeping detailed records for several years and they typically do gain weight and shell length over the winter during their growing years, which was a bit of a surprise initially for me too, but then not so much when the are full grown, then they have been within a couple percentage plus or minus, which is probably more just more a measure of hydration at the time of weigh in because both weights are empty gut.
Intuitively you would think that sense their metabolism is nearly at a standstill, so would growth, but it's not.
Initially one of my theories was that they must be "snacking" on bugs and worms underground at the front end and back end of brumation when temps were moderating, because for the last several years I brumated in soil from outdoor pens, but then I realized that before I had burmated in peat (bug and worm free) and the growth data was the same.
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Jeff Benfer
1.0 cinnamon pastel Python regius
1.1 pastel Python regius
1.1 mojave Python regius
0.3 normal Python regius
1.3 Terrapene carolina thriunguis
2.3 Terrapene carolina carolina
4.1 Kinosternon baurii
1.1 Malaclemys terrapin terrapin
2.2 double het albino and anerythristicThamnophis sirtalis parietalis
1.0 anerythristic Thamnophis sirtalis parietalis
2.3 Iowa snow Thamnophis radix
0.2 het Christmas albino Thamnophis radix
1.1 double het cherry erythristic, albino Thamnophis sirtalis sirtalis
1.1 melanistic Thamnophis sirtalis sirtalis
2.0 66% het snow Thamnophis sirtalis sirtalis
1.2 flame Thamnophis sirtalis sirtalis
1.1 triple heterozygous for amelanistic,carmel, and stripe Pantherophis guttatus
0.1 anerythristic motley Pantherophis guttatus
0.1 butter p.h. stripe Pantherophis guttatus
0.1 carmel stripe p.h. amel Pantherophis guttatus
0.1 amelanistic p.h. carmel,stripe Pantherophis guttatus