Water quality requirements for first-feeding in marine fish larvae of the Cape of Good Hope, with description of developmental stages

Doctoral Thesis


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University of Cape Town

The tolerance of marine fish larvae to NH₃, NO₂⁻, NO₃⁻, H⁺, OH⁻, O₂, and CO₂ was investigated using the decrease in first-feeding incidence following a 24-h exposure as the criterion of response. Ten species, all hatched from pelagic eggs collected at sea, were used in the studies: two soleids (Heteromycteris, Synaptura), a cynoglossid (Trulla), a gadid (Gaidropsarus), a congiopodid (Congiopodus), four sparids (Diplodus, Lithognathus, Pachymetopon, and an unidentified species), and a centracanthid (Pterosmaris). Concentrations that inhibited first-feeding are compared to 24-h LC 50's for the same species, and to concentrations that are known to induce lethal and sublethal responses in other teleost species. Judging from their effect on first-feeding, un-ionized ammonia, elevated pH, and reduced oxygen concentration are considered to be potential hazards in the rearing tank. NO₂⁻, NO₃⁻, H⁺, and free CO₂ are nontoxic at levels likely to be encountered in practical fish culture. There are only minor inter-specific differences in calculated 24-h first-feeding EC 50's (concentration that reduces first-feeding incidence by 50%), which suggests general applicability of the results to a wide variety of first-feeding marine fish larvae. Data are presented on the age at first-feeding and point-of-no-return. The suitability of assorted micro-particles (including the rotifer, Proales, and Pine pollen) as experimental foods is discussed.

Bibliography: pages 259-272.