Diets of juvenile hybrid striped bass (Percichthyidae: Morone chrysops ♀ x M. saxatilis ♂)

In many areas of the United States, striped bass (Morone saxatilis) area prized sport and food fish. Due to difficulties establishing spawning broodstock in reservoirs and lakes, many states have started stocking fingerlings produced via artificial spawning and raised in hatchery ponds. With dwindling availability of striped bass females, the production of hybrid striped bass based on white bass females ( often called sunshine bass or reciprocal cross hybrid striped bass, Morone chrysops ~ x M. saxatilis d') has increased greatly. However, variable survival and growth of juvenile sunshine bass (white bass Morone chrysops ~ x striped bass M saxatilis d' [Percichthyidae]) are problems for hatchery managers. This variability has been attributed to pond temperature fluctuations, fry stocking stress mortality, inadequate pond water quality, food availability, and even predation on fry by cyclopoid copepods. GEIGER et al. (1985) examined the diets o f striped bass larvae and found that fish 8-9 mm long consumed mainly adult copepods ( 69% ), with copepod nauplii and daphnid cladocerans comprising the remainder of the stomach contents. Striped bass (Morone saxatilis) larvae are typically stocked in to rearing ponds at 8-1 O mm in length whereas sunshine bass fry are usually stocked at 2-6 mm, so the early diet of sunshine bass fry should be limited to smaller organisms such as rotifers (Lunwm et al. 1998). LUDWIG (1994), DENSON & SMITH (1997), and LUDWIG & LoCHMANN (2000) report that their laboratory experiments feeding sunshine bass fry rotifers (e.g., Brachionus) and Artemia plus prepared feed yielded fry survival rates ranging from 21.2 to 67.2 %. However, few studies have examined the early diets of fish fry in natural waters or pond rearing systems, so little is known abou t diets o f hybrid striped bass fry or juveniles. In this study, we compared the diets of sunshine bass fry with pond zooplankton composition to determine whether food availability in the rearing ponds at 2 hatcheries affects fish diets, growth, and survival.