Comparison of three fish-loading systems to harvest food-size channel catfish (Ictalurus punctatus)

Three fish-loading systems were used to harvest food-size channel catfish (Ictalurus punctatus). Loading rates of equipment and their effect on post-harvest fish survival and weight gain during cool and warm weather were studied.

The turbine pump loading rate (300·7 kg/min) was greater than the lift net (158·00 kg/min) and vacuum pump (54·1 kg/min), while the lift net was greater than the vacuum pump (p < 0·05).

Mean survivals (± SD) for catfish loaded by lift net, turbine pump and vacuum pump from earthen ponds during cool and warm weather were 96·6% (±2·8), 93·9% (±7·4) and 97·7% (±1·1) and 94·0% (±5·7), 85·3% (±8·6) and 89·0% (±12·5), respectively. Mean weight change (± SD) per catfish loaded by the same equipment during cool-and warm-weather tests were −8·2 g/fish (±31·1), −12·4 g/fish (±15·2) and −17·5 g/fish (±19·9), and 67·6 g/fish (±60·6), 33·9 g/fish (±137·4) and 32·4 g/fish (±142·1), respectivley. There were no significant differences among loading systems for survival or mean weight change per fish. The turbine pump is a possible alternative to the traditional life net as a means of loading food-size channel catfish. Further testing on commercial catfish farms is required.     

Genetic covariation in production traits of sub-adult black bream Acanthopagrus butcheri after grow-out

Predicting the suitability and reliability of traits associated with juvenile growth as indirect selection criteria for choosing future broodstock requires accurate and repeatable estimates of genetic (co)variation for growth traits at different ages. We compared juvenile wet weight of black bream Acanthopagrus butcheri (Munro) at 6 months of age with wet weight, dressed weight, fillet yield and gonad weight in tagged individuals at 18 months of age, following 12 months of farm grow‐out. Fish survival and tag retention was high, and there was significant among‐family variation for all traits. The phenotypic correlations among wet weight, dressed weight and fillet yield at 18 months of age were very high (0.93–0.97) and similar to their genetic correlations (0.96). Importantly, the phenotypic correlations between wet weight at 6 months and wet weight, dressed weight and fillet yield at 18 months were high (0.63–0.65), and so too were their genetic correlations (0.66–0.73), indicating the potential for using wet weight in the hatchery as a selection criterion for improved weight and meat yield of fish at harvest. Gonad weight shared little or no phenotypic or genetic correlation with these other traits, suggesting that selection for faster growing fish will not affect fecundity or sexual maturation rate. It appears, however, that cultured black bream do become sexually mature more rapidly than wild fish, as 78% of all fish harvested in this study had developing or mature gonads, whereas less than 50% of fish in wild populations are reproductively mature by the same age. Precocious sexual development may lead to uncontrolled spawning in grow‐out ponds and a potential loss of selection gains.     

Reserve effect of a small North-East Atlantic marine protected area (Arrábida,Portugal) on soft-sediment fish species

1. The implementation of marine protected areas (MPAs) has been widely used as a tool to manage and conserve marine resources and services. Yet, to date, the reserve effect is still weakly evaluated, particularly for soft-sediment habitats.
2. The Arrábida MPA, considered as a biodiversity hotspot, was fully established in 2009 on the west coast of Portugal and is characterized by large expanses of soft-sediment habitats. This MPA was established to protect biodiversity and to ensure the livelihood of the local small-scale fisheries community.
3. Beyond before–after-control–impact (BACI) analyses were carried out on catch data (abundance and biomass) of 351 trammel net sets from experimental fishing campaigns (2007–2019) to study the reserve effect on demersal fish populations.
4. The results show a declining trend in abundance inside and outside the protected area, with significant positive effects only found for undersize commercial species and Solea senegalensis, and a general increase in fish species total length. Despite the lack of any obvious reserve effect, the increase in fish length can be considered as a first sign.
5. Anthropogenic pressures are generalized around the area, and transgressions of the restrictions are frequently observed inside the no-take zone. These can, among other aspects, delay or prevent the expected reserve effects. Therefore, enforcement and/or modification of the spatial plan must be incentivized to achieve the goals of the MPA.

     

Oyster greening by outdoor mass culture of the diatom Haslea ostrearia Simonsen in enriched seawater

Oyster greening was first described in the seventeenth century as a natural phenomenon. However, it has recently been discovered that the diatom Haslea ostrearia Simonsen causes greening by synthesis of a blue pigment designated as ‘marennine’. This phenomenon, which involves massive proliferation of H. ostrearia in oyster ponds, was not understood or controlled by oyster farmers in the Marennes‐Oléron region (Atlantic coast of France). As greening oysters improved their market value, they tried to develop empirical methods to guarantee oyster fattening and improve profits. In this context, the present study investigated the feasibility of mass culture of diatoms outdoors in 10‐m³ ponds, using enriched seawater. Different biotic and abiotic parameters were monitored daily to determine the influence of the day–night temperature range. After 8 days, H. ostrearia was the dominant diatom species (66%), reaching a mean cell concentration of 2 × 10⁵ cell mL^?1 and a marennine concentration of 3.4 mg L^?1. Although intensive greening was obtained, further studies are required to optimize the production stages before this technology can be transferred to oyster farmers.     

Action of Clathrodin and Analogues on Voltage-Gated Sodium Channels

Clathrodin is a marine alkaloid and believed to be a modulator of voltage-gated sodium (Na_V ) channels. Since there is an urgent need for small molecule Na_V channel ligands as novel therapeutics, clathrodin could represent an interesting lead compound. Therefore, clathrodin was reinvestigated for its potency and Na_V channel subtype selectivity. Clathrodin and its synthetic analogues were subjected to screening on a broad range of Na_V channel isoforms, both in voltage clamp and patch clamp conditions. Even though clathrodin was not found to exert any activity, some analogues were capable of modulating the Na_V channels, hereby validating the pyrrole-2-aminoimidazole alkaloid structure as a core structure for future small molecule-based Na_V channel modulators.