Mortality, growth and swim bladder stress syndrome of sea bass ( Dicentrarchus labrax) larvae under varied environmental conditions

Abstract

Responses to variations in light, temperature and salinity by sea bass larvae are described here. Massive mortality of larvae has been common in Mediterranean culture efforts. This mortality, associated with swim bladder malfunction, has been analysed regarding its association with individual stresses. Optimum temperatures for sea bass growth are clearly unsuited to larval rearing, while brackish sea water (25‰) just as clearly improves growth and survival. Light and nutritional regimes as well as water quality are other sources of environmental stress that may induce the swim bladder stress syndrome (SBSS) and reduce growth and survival. SBSS should not be confused with “gas bubble” disease and its most effective treatment depends on an understanding of larval environmental requirements. Larval growth was enhanced by both decreased salinity and increased temperature, but not by increased light. SBSS and mortality were avoided only when larvae were held at ambient temperature (12.5°C), natural light, and reduced salinity (25‰). Larvae dying with distended swim bladders also had other symptoms of environmental stress—spinal abnormalities, calculi in the urinary bladders, copious mucous and opaque (edemous) tissues. Elevations of temperature and light, as well as ambient sea water (36‰) are environmental stressors and induce SBSS.