Egg production of turbot, Scophthalmus maximus, in the Baltic Sea

• In the brackish water Baltic Sea turbot spawn at ~6–9 psu along the coast and on offshore banks in ICES SD 2324–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic 24oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old 25eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis 26identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of 27fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an ad- 28ditional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy 29for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity 30and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those 31from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05±0.03 mm diameter and 3246.8±6.5 μg dry weight; mean±sd). The difference in egg production matched egg survival probabilities 33in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer repro- 34ductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the 35limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring 36survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting 37spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is 38discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific 39year-classes, and effects of maturation status of sampled fish.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

Reproductive potential Fecundity Egg size Salinity gradient Spawning fishery Life-history traits

Biology (HGO)

Biologi (HGO)

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