The effect of diet quality on reproduction and energy storage in bivalves has not been widely investigated. Food quality and quantity influences reproductive success in many bivalve species, and the timing and rate of reproductive maturation is a dominant influence on natural population dynamics, whereas understanding and controlling reproduction is vital for the reliable production of juvenile mussels for aquaculture. In this study, adult mussels were fed for six weeks on 1 of 4 diets: (1) raw seawater; and raw seawater plus equivalent dry weights of (2) Chaetoceros calcitrans, (3) Pavlova lutheri, and (4) a 1:1 combination of the 2 species. Chaetoceros calcitrans has a higher proportion of simple sugars and sterols compared with P. lutheri, whereas P. lutheri has greater proportions of DHA. Diet composition had a significant effect on the glycogen concentration and reproductive indicators at the end of six weeks. The combined C. calcitrans and P. lutheri supplement showed no change in glycogen stores after 6 wk, however a greater percentage of animals spawned, and a greater proportion of vitellogenic and atretic mussels were produced. Mussels supplemented with C. calcitrans increased glycogen stores and produced greater proportions of mussels with vitellogenic oocytes. Those supplemented with P. lutheri produced a greater proportion of mussels with atretic oocytes, and a lower proportion of D-veliger larvae produced from the eggs. Mussels fed with raw seawater produced a greater proportion of resting mussels, and a lower percentage of mussels spawned at the end of the conditioning period. Oocyte diameter and fecundity showed no significant difference among diets. These results show that diet quality directly influences the allocation of energy to glycogen storage and gametogenesis, however, the mechanism by which this occurs is unclear. Investigation into the allocation of individual biochemical components to each of these processes would further illuminate the process by which diet quality influences the allocation of energy to glycogen storage versus gametogenesis.