Bovine placental lactogen invokes rapid growth in chinook salmon

The effect of recombinant bovine placenta) lactogen (rbPL) treatment upon growth of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum) (14.0 ± 0.31 g wet wt), was examined over a period of 6 weeks. Experimental animals were either injected (5 μg rbPL g−1 week−1), implanted with a cholesterol pellet containing 0.4 mg rbPL (approximately 4 μg g−1 week−1), or orally and rectally intubated with 7.5 μg rbPL g−1 week−1. Control animals were injected with bovine serum albumen (BSA), 5 μg g−1 week−1, implanted with a placebo or orally intubated (7.5 μg BSA g−1 week−1). Significant (P < 0.05) growth acceleration was recorded for rbPL-injected and pellet-implanted groups from week 2 onwards when compared against all other groups. Oral or rectal intubation of rbPL (7.5 μg rbPL g−1 week−1), however, was without effect. Condition factor decreased in all groups, but was significantly lower in rbPL-injected and pellet-implanted fish at trial end when compared against controls. No differences were recorded between groups for per cent body moisture or relative gut length. Hepatosomatic index was significantly (P < 0.05) higher in rbPL-injected and rbPL-implanted chinook salmon versus other fish.