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.

Immunoassays, optical and electrochemical immunosensorsfor tetrodotoxin determination in puffer fish samples

Tetrodotoxin (TTX) is a low molecular weight and potent marine neurotoxin which is usually present in some species of puffer fish. TTX selectively binds to voltage-sensitive sodium channels (VSGCs), blocking the influx of sodium into the cell and affecting neural transmission. The bioaccumulation of this toxin in seafood can poses a risk to human safety. With the purpose of achieving cheap, specific and reliable tools to determine TTX in puffer fish samples, a self-assembled dithiol-based immunoassay, an electrochemical immunosensor and an optical Surface Plasmon Resonance (SPR) immunosensor are proposed. The immunoassay for TTX based on the use of dithiols self-assembled on maleimide-plates (mELISA) has been able to detect as low as 2.28 μg/L of TTX. The effect of different puffer fish matrixes on this mELISA has been quantified and the corresponding correction factors have been established. This
mELISA has enabled to establish the cross-reactivity factors for four TTX analogues: 5,6,11-trideoxy-TTX, 5,6,11-trideoxy-4-anhydro-TTX, 11-nor-TTX-6-ol and 5,11-deoxy-TTX. The crossreactivity factors have also been established by the optical SPR immunosensor previously reported, which had a limit of detection (LOD) of 4.27 μg/L. The mELISA and the SPR immunosensor have then been tested with spiked-puffer fish matrixes, providing an effective
LOD of 0.23 and 0.43 mg/kg respectively, well below the limit set in Japan (2 mg/kg). The mELISA and the SPR immunosensor have also been applied to the analysis of naturally contaminated puffer fish samples, providing similar TTXs contents between techniques and also compared to LC-MS/MS. The suitability of these immunochemical techniques has been demonstrated not only for screening purposes, but also for research activities. Currently, given that dithiols could improve the electron transfer and the sensitivity of an electrochemical assay, the mELISA strategy is being transferred to gold electrodes for the electrochemical detection of TTX and the subsequent development of the multiplexed electrochemical immunosensor.