Data from: Direct effects of microalgae and protists on herring (Clupea harengus) yolk sac larvae

This study investigated effects of microalgae (Rhodomonas baltica) and heterotrophic protists (Oxyrrhis marina) on the daily growth, activity, condition and feeding success of Atlantic herring (Clupea harengus) larvae from hatch, through the end of the endogenous (yolk sac) period. Yolk sac larvae were reared in the presence and absence of microplankton and, each day, groups of larvae were provided access to copepods. Larvae reared with microalgae and protists exhibited precocious (2 days earlier) and ≥ 60% increased feeding incidence on copepods compared to larvae reared in only seawater (SW). In the absence and presence of microalgae and protists, survival and growth trajectories of yolk sac larvae were similar and digestive enzyme activity (trypsin) and nutritional condition (RNA-DNA ratio) markedly declined in all larvae directly after yolk sac depletion. Thus, microplankton promoted early feeding but was not sufficient to alter survival and growth during the yolk sac phase. Given the importance of early feeding, field programs should place greater emphasis on the protozooplankton-ichthyoplankton link to better understand match-mismatch dynamics and bottom-up drivers of year class success in marine fish

S1_dataset

This study investigated effects of microalgae (Rhodomonas baltica) and heterotrophic protists (Oxyrrhis marina) on the daily growth, activity, condition and feeding success of Atlantic herring (Clupea harengus) larvae from hatch, through the end of the endogenous (yolk sac) period. Yolk sac larvae were reared in the presence and absence of microplankton and, each day, groups of larvae were provided access to copepods. Larvae reared with microalgae and protists exhibited precocious (2 days earlier) and ≥ 60% increased feeding incidence on copepods compared to larvae reared in only seawater (SW). In the absence and presence of microalgae and protists, survival and growth trajectories of yolk sac larvae were similar and digestive enzyme activity (trypsin) and nutritional condition (RNA-DNA ratio) markedly declined in all larvae directly after yolk sac depletion. Thus, microplankton promoted early feeding but was not sufficient to alter survival and growth during the yolk sac phase. Given the importance of early feeding, field programs should place greater emphasis on the protozooplankton-ichthyoplankton link to better understand match-mismatch dynamics and bottom-up drivers of year class success in marine fish

Mean (±S.E., n = 3 tanks) standard length (a), dry weight (b) and standardized RNA-DNA ratio (c) versus age (days post hatch, dph) in yolk sac larval herring (<i>Clupea harengus</i>) reared in the absence or presence of microalgae (RB) and protists (OX).

<p>Significant differences between treatments were observed in standard length (panel a, P = <0.001, one-way repeated measures ANOVA on ranks) and dry weight (panel b, P = <0.001, one-way repeated measures ANOVA). The black arrow indicates the age of complete yolk absorption. The letter ‘I’ represents the initial (common) measurement at 0 dph.</p

Estimating post-release mortality of European sea bass based on experimental angling

European sea bass (Dicentrarchus labrax) is an important target species for recreational and commercial fisheries. In recent years, the spawning stock biomass has declined markedly in some areas, and strict management measures have been introduced. However, the development of appropriate stock assessment and fisheries management has been hampered by a lack of information on post-release mortality. This study investigated post-release mortality of sea bass captured with common recreational fishing gear under experimental conditions in an aquaculture facility over 10 d. Three experiments investigated: (i) the effects of different bait types; (ii) the impact of prolonged air exposure; and (iii) the impact of deep hooking on post-release mortality. By combining the experimental results with country-specific information on sea bass angling practices, estimates of post-release mortality are provided for the northern sea bass stock. No mortality was observed for sea bass captured on artificial baits. The use of natural baits resulted in a mortality of 13.9% (95% CI = 4.7-29.5%), which was associated with deep hooking, hooking injuries, and prolonged air exposure. The use of artificial baits and short air exposure (°30 s) increased survival probability, whereas deep hooking resulted in 76.5% (95% CI 50.0-93.2%) mortality. Depending on country-specific angling practices, post-release mortality estimates ranged from 2.8% to 9.1% (mean 5.0%, 95% CI 1.7-14.4%) for northern sea bass. Despite these relatively low mortality estimates, post-release mortality should be considered in stock assessments as its cumulative impact may be high. Moreover, post-release mortality can be reduced by implementing species-specific best practice guidelines

Sperm performance limits the reproduction of an invasive fish in novel salinities

Aim The few fish species able to reproduce across wide osmotic ranges either plastically acclimate sperm performance to, or are locally adapted to, different salinities. The invasive round goby (Neogobius melanostomus) is spreading in Eurasia and the Americas, into both fresh and brackish water. We aim to understand if reproduction in different salinities is affected by an ability to acclimate. Location Brackish and freshwater systems of northern Europe and the Baltic Sea. Methods We cross-exposed round gobies of freshwater and brackish origin to 0 and 16 practical salinity units (PSU), and the fish were given nest boxes in which to spawn. After 4 weeks, we measured their sperm performance in both 0 and 16 PSU; fertilization success of each egg clutch was measured through visual analysis of eggs. Clutches were split and allowed to develop in both 0 and 16 PSU salinity, and reproductive success (zygote development) was measured 20 ± 1 days later. Responses were analysed using generalized mixed models. Results After a month, the fish showed no plasticity in sperm performance to their acclimation salinity, regardless of their origin. Sperm velocity was highest in the salinity similar to the males’ origin. Significantly lower fertilization success was measured for individuals that reproduced outside their salinity of origin despite recurring spawning events in all treatment groups. Among fertilized eggs, zygote development was similar regardless of salinity treatment of either eggs or parents. Main Conclusions Short-term acclimation to new salinities does not affect sperm performance in the round goby. Alternative hypotheses such as local adaption should be further investigated. Limits to the species’ reproductive success, and therefore invasion processes, are likely dependent on environment-phenotype matches. Fish of brackish origin spawned successfully in freshwater, pointing to an increased risk of introducing populations of brackish origin into freshwater