Seasonal changes in broodstock spawning performance and egg quality in ballan wrasse (Labrus bergylta)

Sea lice continue to be one of the largest issues for the salmon farming industry and the use of ballan wrasse (Labrus bergylta) as a biological control is considered to be one of the most sustainable solutions in development. Broodstock management has proved challenging in the initial phases due to the significant lack of understanding of basic reproductive physiology and behaviour in the species. The aim of the study was to monitor captive breeding populations throughout a spawning season to examine timing and duration of spawning,quantify egg production, and look at seasonal changes in egg quality parameters as well as investigate the parental contribution to spawning events. A clear spawning rhythm was shown with 3-5 spawning periods inclusive of spawning windows lasting 1-9 days followed by inter spawning intervals of 8-12 days. Fertilization rate remained consistently high (> 87.5%) over the spawning season and did not differ significantly between spawning populations. Hatch rate was variable (0-97.5 %), but peaked in the middle of the spawning season. Meanoocyte diameter and gum layer thickness decreased slightly over the spawning season with no significant differences between spawning populations. Fatty acid (FA) profile of eggs remained consistent throughout the season and with the exception of high levels of ARA (3.8 ± 0.5 % of total FA) the FA profile was similar to that observed in other marine fish species. Parental contribution analysis showed 3 out of 6 spawning events to be single paired mating while the remaining 3 had contributions from multiple parents. Furthermore, the proposed multiple batch spawning nature of this species was confirmed with proof of a single femalecontributing to two separate spawning events. Overall this work represents the first comprehensive data set of spawning activity of captive ballan wrasse, and as such and will be helpful in formulating sustainable broodstock management plans for the species.

Development of release methods for critically endangered freshwater pearl mussels (Margaritifera margaritifera)

Biodiversity loss is a global problem with freshwater bivalves considered amongst the most<br/>endangered biota. The freshwater pearl mussel, Margaritifera margaritifera, is declining<br/>throughout its range owing to habitat degradation and overexploitation. In most of its range,<br/>populations are regarded as reproductively non-functional which has led to the development<br/>of captive breeding programmes. A novel method of releasing M. margaritifera was trialled,<br/>with captive-bred juveniles being released into the rivers caged in ‘mussels silos’ (protective<br/>concrete domes with ventilation creating upwelling to ensure water through flow). We<br/>released 240 juvenile mussels and survival and growth rates were monitored for 18 months<br/>post-release for three size classes: A (13.01-20.00mm); B (10.01-13.00mm); and C (4.01-<br/>10.00mm). We explicitly tested two experimental treatments; one where sediment was added<br/>to each silo (allowing mussels to orientate and burrow) and one without sediment. Survival<br/>by the end of the experiment at month 18 was significantly higher for the largest size class at<br/>97% (though growth was lowest in this cohort), and lowest for the smallest size class at 61%<br/>(though growth was highest in this cohort). Survival and growth were unaffected by the<br/>experimental treatment suggesting that adding sediment offered no advantage. Growth was<br/>positively correlated with both water temperature and the particle size of suspended solids<br/>(both of which were collinear, peaking in summer). There are a large number of ex situ<br/>breeding programmes for freshwater pearl mussels throughout Europe and our finding<br/>suggest that the use of ‘mussel silos’ could be a useful tool to protecting juvenile mussels<br/>allowing them to be released at a relatively early stage of development, minimising the risk of<br/>domestication.