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Effective treatment of larval bacterial diseases is a difficult problem when
culturing ornamental fish. Oral administration of antibiotics using existing
microparticle types is not effective due to high leakage rates; furthermore, injection of
larvae is not practical. Treatment is currently limited to use of antibiotic baths, . In this
study, we evaluated lipid spray beads (LSB) for delivery of the low-molecular weight,
water-soluble antibiotic, oxytetracycline·HCl (OTC) to fish larvae. Lipid spray beads
composed of menhaden stearine have shown good retention of water-soluble core
materials and high acceptability by larval fish. Various OTC core-to-lipid ratios and
OTC core concentrations were evaluated to maximize OTC delivery efficiencies.
Acceptability and digestion of LSB containing riboflavin by larval zebrafish, Danio
rerio (Hamilton), and larval gobies, Asterropteryx semipunctata (Rüppell), were also
evaluated.
Increasing LSB core-to-lipid ratios from 1:3 v/v to 1:1 v/v resulted in an
increase of encapsulation efficiency from 2.33% w/w to 3.68% w/w. LSB prepared
with a ratio of 1:1.25 v/v were then used to determine the effect of core concentration
on encapsulation, retention and delivery efficiencies. Increasing concentrations of
OTC in the core from 0.1 to 0.5 g OTC mL-1 H2O caused encapsulation efficiencies to
increase from 3.95% w/w to 18.77% w/w, respectively. This increase did not affect
retention efficiencies and improved delivery efficiencies. Lipid spray beads prepared
with a core concentration of 0.5 g OTC mL-1 H2O produced the highest delivery
efficiencies (7.9 ± 0.7% w/w) after suspending the beads in water for 60 min60 min
aqueous suspension
Consumption of LSB containing OTC by first-feeding zebrafish and goby
larvae was confirmed by analysis of feeding incidence and gut fullness. Visual
observations of larvae fed on LSB containing riboflavin indicated that LSB were
digested by larvae of both species. Particles were compacted and brightly fluorescent,
freely-dissolved riboflavin filled the gut lumen and exited the anus in plumes. These
results suggested that LSB composed of menhaden stearine could be used to deliver
OTC to larval fish and may be useful in treating larval fish infected with bacteria
susceptible to OTC. Oxytetracycline dosage could be controlled by either varying the
concentration of administered LSB or the concentration of core solution. |
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