Investigating the metabolic and oxidative stress induced by biofouled microplastics exposure in Seriola lalandi (yellowtail kingfish).

Microorganisms quickly colonise microplastics entering the ocean, forming a biofilm that, if ingested, is consumed with the microplastics. Past research often neglects to expose fish to biofouled microplastics, opting only for clean microplastics despite the low likelihood that fish will encounter clean microplastics. Here, we investigate the physiological impacts of biofouled polyethylene microplastic (300-335 µm) exposure in juvenile fish. Intermittent flow respirometry, antioxidant enzyme activity, and lipid peroxidation were investigated after fish were exposed to clean, biofouled, or no microplastic beads. Fish exposed to biofouled microplastics had a wider aerobic scope than those exposed to clean microplastics while antioxidant enzyme and lipid peroxidation levels were higher in clean microplastics. Clean microplastic exposure indicated higher fitness costs, potentially due to a nutritional advantage of the biofilm or varying bioavailability. These findings highlight the importance of replicating natural factors in exposure experiments when predicting the impacts of increasing pollutants in marine systems.

Investigating the impacts of biofouled marine plastic debris on the olfactory behaviour of juvenile yellowtail kingfish (Seriola lalandi).

Marine microplastics are rapidly colonised by a microbial community which form a biofilm unique from the surrounding seawater that often contains infochemical-producing species associated with food sources. Here, we investigated whether juvenile kingfish (Seriola lalandi) were more attracted to biofouled plastics compared to clean plastics. Plastics were exposed to unfiltered seawater for one month to cultivate a microbial community. An olfactory behavioural experiment showed little difference in their response to the biofilm compared to clean plastic and control treatment. Further, ingestion experiments demonstrated that S. lalandi ingested fewer biofouled microplastics compared to clean microplastics. However, this was likely due to the bioavailability of the biofouled microplastics. This study highlights that while juvenile kingfish will ingest microplastics, they are not more attracted to those with a naturally acquired biofilm.

Elevated temperature and CO2 have positive effects on the growth and survival of larval Australasian snapper.

Rising water temperature and increased uptake of CO2 by the ocean are predicted to have widespread impacts on marine species. However, the effects are likely to vary, depending on a species' sensitivity and the geographical location of the population. Here, we investigated the potential effects of elevated temperature and pCO2 on larval growth and survival in a New Zealand population of the Australasian snapper, Chrysophyrs auratus. Eggs and larvae were reared in a fully cross-factored experiment (18 °C and 22 °C/pCO2 440 and 1040 µatm) to 16 days post hatch (dph). Morphologies at 1 dph and 16 dph were significantly affected by temperature, but not CO2. At 1dph, larvae at 22 °C were longer (7%) and had larger muscle depth at vent (14%), but had reduced yolk (65%) and oil globule size (16%). Reduced yolk reserves in recently hatched larvae suggests higher metabolic demands in warmer water. At 16 dph, larvae at elevated temperature were longer (12%) and muscle depth at vent was larger (64%). Conversely, survival was primarily affected by CO2 rather than temperature. Survivorship at 1 dph and 16 dph was 24% and 54% higher, respectively, under elevated CO2 compared with ambient conditions. Elevated temperature increased survival (24%) at 1 dph, but not at 16 dph. These results suggest that projected climate change scenarios may have an overall positive effect on early life history growth and survival in this population of C. auratus. This could benefit recruitment success, but needs to be weighed against negative effects of elevated CO2 on metabolic rates and swimming performance observed in other studies on the same population.

Organ health and development in larval kingfish are unaffected by ocean acidification and warming.

Anthropogenic CO2 emissions are causing global ocean warming and ocean acidification. The early life stages of some marine fish are vulnerable to elevated ocean temperatures and CO2 concentrations, with lowered survival and growth rates most frequently documented. Underlying these effects, damage to different organs has been found as a response to elevated CO2 in larvae of several species of marine fish, yet the combined effects of acidification and warming on organ health are unknown. Yellowtail kingfish, Seriola lalandi, a circumglobal subtropical pelagic fish of high commercial and recreational value, were reared from fertilization under control (21 °C) and elevated (25 °C) temperature conditions fully crossed with control (500 µatm) and elevated (1,000 µatm) pCO2 conditions. Larvae were sampled at 11 days and 21 days post hatch for histological analysis of the eye, gills, gut, liver, pancreas, kidney and liver. Previous work found elevated temperature, but not elevated CO2, significantly reduced larval kingfish survival while increasing growth and developmental rate. The current histological analysis aimed to determine whether there were additional sublethal effects on organ condition and development and whether underlying organ damage could be responsible for the documented effects of temperature on survivorship. While damage to different organs was found in a number of larvae, these effects were not related to temperature and/or CO2 treatment. We conclude that kingfish larvae are generally vulnerable during organogenesis of the digestive system in their early development, but that this will not be exacerbated by near-future ocean warming and acidification.

Accommodating the cost of growth and swimming in fish-the applicability of exercise-induced growth to juvenile hapuku (Polyprion oxygeneios).

Induced-swimming can improve the growth and feed conversion efficiency of finfish aquaculture species, such as salmonids and Seriola sp., but some species, such as Atlantic cod, show no or a negative productivity response to exercise. As a possible explanation for these species-specific differences, a recent hypothesis proposed that the applicability of exercise training, as well as the exercise regime for optimal growth gain (ERopt growth), was dependent upon the size of available aerobic metabolic scope (AMS). This study aimed to test this hypothesis by measuring the growth and swimming metabolism of hapuku, Polyprion oxygeneios, to different exercise regimes and then reconciling the metabolic costs of swimming and specific dynamic action (SDA) against AMS. Two 8-week growth trials were conducted with ERs of 0.0, 0.25, 0.5, 0.75, 1, and 1.5 body lengths per second (BL s(-1)). Fish in the first trial showed a modest 4.8% increase in SGR over static controls in the region 0.5-0.75 BL s(-1) whereas the fish in trial 2 showed no significant effect of ER on growth performance. Reconciling the SDA of hapuku with the metabolic costs of swimming showed that hapuku AMS is sufficient to support growth and swimming at all ERs. The current study therefore suggests that exercise-induced growth is independent of AMS and is driven by other factors.

Do swimming fish always grow fast? Investigating the magnitude and physiological basis of exercise-induced growth in juvenile New Zealand yellowtail kingfish, Seriola lalandi.

There is a wealth of evidence showing that a moderate level of non-stop exercise improves the growth and feed conversion of many active fishes. A diverse number of active fish are currently being farmed, and an optimal level of exercise may feasibly improve the production efficiency of these species in intensive culture systems. Our experiments have set out to resolve the growth benefits of juvenile New Zealand yellowtail kingfish (Seriola lalandi) enforced to swim in currents at various speeds over two temperatures (14.9 and 21.1 °C). We also probed potential sources of physiological efficiency in an attempt to resolve how growth is enhanced at a time of high energetic expenditure. Results show that long-term exercise yields a 10% increase in growth but this occurs in surprisingly low flows (0.75 BL s⁻¹) and only under favourable environmental temperatures (21.1 °C). Experiments using a swim flume respirometer indicate that exercise training has no effect on metabolic scope or critical swimming speeds but it does improve swimming efficiency (lower gross costs of transport, GCOT). Such efficiency may potentially help reconcile the costs of growth and exercise within the range of available metabolic energy (scope). With growth boosted in surprisingly low flows and elevated water temperatures only, further investigations are required to understand the bioenergetics and partitioning of costs in the New Zealand yellowtail kingfish.