Dietary creatine and guanidinoacetic acid supplementation have limited effects on hybrid striped bass.

The effects of dietary supplementation of creatine and guanidinoacetic acid (GDA) have been studied to a limited extent in various fish species including red drum (Sciaenops ocellatus) and hybrid striped bass (HBS) (Morone saxatilis x M. chrysops). However, in HSB, there is a need to better understand the impact of creatine and GDA supplementation at elevated salinity which may be encountered by this euryhaline fish. Therefore, two separate feeding trials were conducted at a salinity ranging from 15 to 20 g/L with juvenile HSB for 9 and 8 weeks to evaluate the effects of dietary creatine and GDA. In each trial, four diets were formulated with either singular additions of creatine at 2% of dry weight, GDA at 1% of dry weight, or a combination of both. Fish grew adequately in both feeding trials but no significant (P > 0.05) effects of supplemental creatine or GDA were observed on weight gain, feed efficiency, survival, hepatosomatic index (HSI), intraperitoneal fat (IPF ratio), or protein conversion efficiency (PCE). However, fish fed diets supplemented with creatine had significantly (P < 0.05) increased ash and reduced lipid deposition in whole-body tissues in the first feeding trial. Supplemental creatine also resulted in significantly higher muscle yield in the second trial, but no other effects on growth performance or body composition were observed. The addition of GDA to the diet had little effect except for significantly increasing the creatine content in the liver of fish in both feeding trials due to its role as a precursor and a catalyst for synthesis of creatine within the body. Based on the results of these two trials, supplemental creatine and GDA had rather limited effects on HSB cultured in moderately saline water.