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Growth and reproductive traits of diploid and triploid forms of the Squalius alburnoides cyprinid complex in a tributary of the Guadiana River, Portugal

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The Squalius alburnoides hybrid complex has diploid, triploid and some rare tetraploid male and female forms, with triploid females predominating in most populations. The reproductive traits of diploids and triploids from a population in a tributary of the Guadiana River, Portugal, were compared, during a two-years period. Few differences were found in the growth and reproductive traits of diploid and triploid females. Marginal differences were found in the longevity, with a few triploid females living up to six years compared with a maximum of five years for diploid females and a maximum of four years for diploid males. Both diploid and triploid females exhibited rapid growth in the first two years of life followed by rapid drop off linked to attaining sexual maturity. Reproductive effort increased with age but was mainly linked to number of eggs produced and not to egg size, since oocyte size did not vary with age or length of fish in either ploidy forms. Both forms exhibited a protracted spawning period between March and June, suggesting multiple-spawning behaviour. Triploid females had a slightly smaller oocyte diameter that may be due to the production of reduced (haploid) oocytes while diploid females produced diploid (unreduced) oocytes The potentially higher production of diploid oocytes (which become triploid eggs after fertilisation) by diploid females could at least partially account for the higher percentage of triploids in natural populations. In addition, the production of bigger (diploid) oocytes, with possibly higher energetic content could lead to bigger fish larvae, which tend to have a higher survival rate. The time of spawning of both diploids and triploids appears to be synchronised, although differences were found in the onset of the spawning period between years, due to annual variations in temperature conditions.
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Keywords: DIPLOID-POLYPLOID COMPLEX; FECUNDITY; GROWTH; GSI; INTERMITTENT STREAM; REPRODUCTIVE; TACTICS.

Document Type: Research Article

Publication date: April 1, 2003

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