THE USE OF CONDITION INDICES IN LARVAL
Mortality of larval fish and invertebrates may potentially be estimated from indices of larval condition or health, on the assumption that lar-vae in poor condition grow slower and are subject to the cumulative effects of starvation, predation or disease. Larval condition integrates feeding success...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.557.2383 http://www.asfb.org.au/pdf/1991/1991-v15-01-06.pdf |
| Summary: | Mortality of larval fish and invertebrates may potentially be estimated from indices of larval condition or health, on the assumption that lar-vae in poor condition grow slower and are subject to the cumulative effects of starvation, predation or disease. Larval condition integrates feeding success of the previous few days and, to the extent this influences growth and mortality, may ultimately determine not only recruitment but also the structure of adult assemblages. This paper briefly reviews morphological, biochemi-cal, otolith and histological condition indices, with specific reference to a comparison of dry weight, lipid and otolith indices of pelagic juve-nile cod (Gadus morhua). Morphological indi-ces such as body depth or dry weight are simple, but are often insensitive, and require shrinkage correction for the early larvae. Biochemical indices such as RNAPNA ratio appear to be equivalent across species, but require sorting of the larvae at sea before rapid freezing. The peripheral increment widths of the otolith are a simple measure of recent growth, while histo-logical measurements of the gut epithelium or muscle cell diameter represent a direct index of starvation mortality. Validation of indices is necessary, but cau-tion is advised when extrapolating from reared larvae to the field. The within-larva correlation of many indices is low or not significant prob-ably due to varying temporal responses to star-vation of each index. In general, condition indi-ces must be tailored to the species and the size (or stage). There are very few Australasian studies of larval condition. The relative high diversity and low density of Australian fish larvae, requires indices to be equivalent across species to assess the impact of oceanographic features or events. |
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