Production of antifreeze glycoproteins in cultured and wild juvenile Atlantic cod (Gadus morhua L.) in a common laboratory environment
Background:
Cold-ocean fishes produce blood-borne antifreeze proteins or glycoproteins with affinity to bind embryonic ice crystals and prevent growth = depress freezing point 200-300x
Also protects cells from depolarization and subsequent damage at low (non-freezing) temps
Hypotheses:
Cultured cod reared @ high water temps/long day lengths not able to produce AFGPs
Cod from southern end of distribution produce less AFGPs than more northern cod
Methods:
Cultured cod from Grand Banks (more northern) and Gulf of Maine (more southern) parents reared in lab
18h day lengths and ~8-12 degrees C
Wild cod (young of the year) collected from Bonavista Bay (more northern) and Fortune Bay (more southern)
All fish starved 48h prior to experiment and then 48h prior to end of experiment
10 chambers with 10 cod from a single population in each
Temp started at 6 degrees C and progressively declined to 1.5 degrees C by the end (14 weeks)
Blood samples taken, plasma separated via centrifuge, nanolitre osmometer used to measure freezing point of single ice crystal in plasma and thereby indirectly estimate amount of AFGPs present by difference between freezing and melting points (thermal hysteresis = function of AFGP production)
Results:
Initially 9/10 cultured cod indicated no presence of AFGPs, majority of wild cod showed presence of AFGPs
By the end nearly all fish producing AFGPs
No difference between GB & GOM or BB & FB AFGP levels
Discussion:
Results show cod from southern and able to produce AFGPs if necessary
Cultured cod (from warmer temps) able to produce AFGPs if necessary
Environmental temp cues AFGP production, higher in juveniles (2-3 degrees C) than adults (0-1 degrees C) due to distribution
Support conclusion that this is genetic since development at warmer temps did not alter ability to produce AFGPs
No evidence to suggest southern cod less able to produce AFGP, but temps were not subzero so may have been relatively lower to southern cod than northern cod
No evidence to suggest low temps necessary during early development for AFGP production later in life