Effect of Timing of Oil Film Removal and First Feeding on Swim Bladder Inflation Success among Intensively Cultured Striped Bass Larvae

Abstract

Swim bladder inflation success was measured for larval striped bass Morone saxatilis reared under experimental hatchery procedures that typified high-intensity larval rearing facilities. Larvae were stocked into indoor 1.8-m-diameter fiberglass tanks at densities of about 60 fry/L; tanks were supplied with once-through artesian water from a limestone aquifer. The control group of larvae were reared in a tank in which autogenous oil films from decomposing eggs and larvae were removed by oleophilic cloth and the fish were not fed until inflation success exceeded 90%. Experimental larvae were removed from the control group at 4 d posthatch (dph) and either placed in rearing conditions that mimicked the development of autogenous surface oil films or were maintained in tanks in which oil films were removed by oleophilic cloths. Experimental fry were subsequently either fed early (at 4 dph) as their feeding response developed or were not fed until 6 dph when swim bladder inflation was substantially (i.e., >90%) completed within the control group of fry. The effects of surface oil film and of early feeding on final inflation success were tested in a fully cross-classified experimental design with duplicates. Fry reared underneath oil films had relatively low (4.8–11.0%) mean inflation success, regardless of timing of initial feeding events. Fry reared in tanks from which oil films were removed had relatively high (96.6–96.8%) mean inflation success, regardless of timing of initial feeding. Additionally, from 6 to 10 dph, fry with uninflated swim bladders were removed daily from experimental tanks with oil films and subsequently reared in tanks without oil films. Low subsequent inflation success among these fry demonstrated a rapid temporal decline in the capacity for oil removal techniques to promote inflation success. Within 48 h of the completion of inflation in the control group, the proportion of fry with uninflated swim bladders that subsequently inflated under oil-free conditions had decreased to 26.2%. Inflation success, therefore, was strongly influenced by the application and timing of oil film removal techniques but was not strongly affected by preinflation feeding of the larval fish.