Ólöf Dóra Bartels Jónsdóttir

Effects of exposure to extended photoperiods during the first winter on long-term growth and age at first maturity in turbot (Scophthalmus maximus)

The effects of photoperiod on growth of juvenile turbot and the consequences of extended daylength on age at first maturation were investigated. Growth of individually tagged turbot (initial weight 34–44 g, n = 94) was monitored for 18 months. The fish were held under natural photoperiod from hatching (July) until the start of the experiment in December. From December 4, 1991 until May 26, 1992, the fish were reared under constant light (LD24:0, n = 27), 16-h light:8-h darkness (LD16:8, n = 35), or simulated natural photoperiod for 60 °25′N (LDN, n = 32). The fish were then reared together on LDN for 12 months until first maturation during summer 1993 (age 24 months). The fish were held at 16 °C from December 1991 onwards. A growth promoting effect of extended daylength was seen in the LD16:8 and LD24:0 groups, but the effect was not apparent in the LD24:0 group until 6 months after the fish had been transferred to LDN. The final mean weights of the female turbot were 1727 g and 1777 g in the LD16:8 and LD24:0 groups, respectively, whereas final mean weights of males in these groups were 1075 g and 1055 g. In the LDN group the final mean weights for females and males were 1290 g and 909 g, respectively. The results from the present study suggest that exposure to extended photoperiod alters the growth pattern of both maturing fish and immature fish resulting in increased overall growth. Fewer males matured in the LD16:8 (26%) and LD24:0 (17%) groups than in the LDN (56%) group, whereas there were no differences between the experimental groups in the proportion of females that matured (range = 60–63%). It is concluded that extended daylength

Genetic heterogeneity and growth properties of different genotypes of Atlantic cod (Gadus morhua L.) at two spawning sites off south Iceland

Abstract To investigate possible differences in life history traits of Atlantic cod in Icelandic waters, cod were collected at two spawning areas off Southwest Iceland (Loftstaðahraun and Kantur) in two surveys during the spawning season. The sampled fish were measured and age and sex determined. In addition they were analysed for allelic variation at the synaptophysin ( Syp I) locus. Significant differences in growth performance and Syp I genotype distributions were found between the sampling localities. The cod sampled at Loftstaðahraun displayed higher mean weight and length compared to the cod from Kantur and this was mainly related to higher age. Significant differences in genotype ( Syp I) were also observed between cod collected at the two sampling sites. The results indicate that the cod spawning in south Icelandic waters do not belong to one panmictic population and these populations seem to display different life histories.

Linking population genetics and growth properties of Atlantic cod

It is strongly implicated that cod in the NorthAtlantic Ocean is sub-structured at a smallgeographic scale exemplified by studies fromCanadian, Icelandic, and Norwegian waters. Inthe first part of this review, we reviewedpopulation genetics studies in these threeareas and our conclusion is that, despite someinconsistencies in the numerous genetic studiesof cod in Norwegian and Icelandic waters, andthe northwest Atlantic, these studiesillustrate that cod in the investigated areasconsists of several distinct populations, bothwithin and between areas. However, tounderstand the contradictory results obtainedin some of the studies discussed in thisreview, more knowledge about the influence ofnatural selection, mutation, and genetic drifton the genetic material of cod is necessary.Such knowledge could guide us to the markersgiving the best illustration of the geneticstructure in these areas. Identifying andgenetically characterizing wild stocks areessential steps for their conservation, sinceoverexploitation of genetically differentpopulations can lead to the loss of geneticvariability and productivity in subsequentgenerations.Motivated by the hypothesis that growthpatterns may reflect specific genotypeadaptations, we reviewed stock specificresponses on growth in the second part of thisreview and try to link these with the differentlife histories within the different stock unitsindicated in the first part of the review. Anexample of genetically-based differencesbetween population units at two spawninglocalities off south Iceland is discussed.Studies have shown conflicting results,depending on which side of the Atlantic theproblem has been investigated. We propose thata common-garden meta-analysis with several codstocks from both sides of the Atlantic isneeded to give any reasonable answer to thequestion of genetically-based growthdifferences.In this review, we have not tried to quantifyhow large the environmental part of growthregulation is versus the genetic part, as thisinformation is not available in the publishedliterature on cod. Based on recent research ontwo flatfish species (turbot and Atlantichalibut), approximately 30% of growthvariation is caused by genetic factors, but itremains to be seen if this is similar in cod.

Nuclear DNA RFLP variation of Atlantic cod in the North Atlantic Ocean

A total of 551 specimens of Atlantic cod was collected from six locations across the North Atlantic Ocean. The samples were analysed for allelic variation at six nuclear restriction fragment length polymorphism (RFLP) loci scored by five anonymous cDNA clones, and the sequenced and identified synaptophysin (Syp I). Significant differences in allelic variation were found between the sampling localities. The greatest degree of differentiation was detected between the Barents Sea and Scotian Shelf samples vs. the remaining sample units and a clear differentiation between west and east Atlantic samples was found.

Population genetic structure of lumpfish along the Norwegian coast: aquaculture implications

The potential for genetic contamination of stocks arising from translocation and subsequent release or escape of translocated and/or genetically mixed stocks may be a significant risk to wild populations. In this context, we undertook a population genetic survey of stocks of lumpfish (Cyclopterus lumpus) along the Norwegian coast to establish the existing genetic population structure, which will aid the development of policy of the species’ use as cleaner fish in salmonid aquaculture. This was done by using 14 microsatellite loci and 287 specimens collected at five fishing grounds, covering most of the Norwegian coastline from south to north, with additional 18 samples of first-generation reared fish from a fish farm outside Tromsø (North Norway). Overall, there was no indication of significant spatial genetic structuring or of positive correlation between geographic and genetic distance among the wild lumpfish samples. These results suggest that, should translocated individuals escape from aquaculture in Norway, this will probably have little to no impact on the genetic composition of the local fish population.

Correction to: Population genetic structure of lumpfish along the Norwegian coast: aquaculture implications

The original version of this article unfortunately contained an error where the figure caption for Figures 3 and 4 was mixed.