Stocking density and its influence on the productivity of red cusk eel, Genypterus chilensis (Guichenot, 1848), in shallow raceways

We compared the growth properties of red cusk eel Genypterus chilensis with initial mean weight ± standard error, 106.2 ± 6.1 g reared in shallow raceways at three different stocking densities (28.5, 46.1, and 60.7 kg m-3) in a 226-day long growth trial at a constant temperature of 17°C. There was a trend towards higher specific growth rates at the highest density. Final mean weights were 333 ± 12, 352 ± 12, and 354 ± 15 g, at the 30, 45, and 60 kg m-3 density, respectively. Overall, the growth rates were higher in the 60 kg m-3 density group than the two other density groups. The daily feeding intake (%) was higher in the medium (0.51), and high (0.55) density groups compared the low-density group (0.45). Feed conversion efficiency (FCE) did not differ between the density groups. A significant size rank correlation was maintained in all density groups throughout the study. Calculated productivity increased almost linearly with increasing stocking density and was found to be 32, 34, and 39 g m-2 d-1 at 30, 45, and 60 kg m-3, respectively. The results show that the optimum density conditions for farming juvenile red cusk eel, both concerning growth rate, feed conversion, and productivity is at densities equal to or higher than 60 kg m-3.publishedVersio

The effect of alternate-day feeding on growth and feed conversion in Atlantic cod Gadus morhua

This study aimed to investigate the effect of alternating feeding (Alt) compared with control being fed every day (Con) in the on-growth face of Atlantic cod. Individually marked fish (198 and 98 in the Con and Alt groups, respectively) was sampled for weight and length on 6 occasions over a 15-month period, where mean weight increased from 628 and 758 g to 2635 and 3041 g, for the Con and Alt groups, respectively. Feeding alternate day resulted in 13 percentage more weight gain in the alternating feeding group (2283 vs. 2007 g) and improved feed conversion ratio (FCR, 1.07) compared with control (FCR 1.45). The Alt group consumed significantly less feed (27%) compared with control. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days during the on-growing period of Atlantic cod.publishedVersio

Electrical stunning and killing of lumpfish with commercial waterbath and dry stunners

Lumpfish, ranging in size from 146-4200 g, were placed in an electric dry stunning unit head first and exposed to 50 Hz, 240 V AC for 0.5 or 1 s and thereafter 4.5 or 9 s of electricity, thus 5 and 10 s respectively. In seawater, lumpfish were exposed to an electric field equivalent of 4.6 Vrms/cm, 100 pps square AC, with 15% duty cycle for 1 s and thereafter 9 s. This to verify whether the animal is rendered unconscious prior to killing by a throat cut, immersion into cold brine (-14 to -18 °C) or hypoxic water supersaturated with CO2. Behaviour, heart (ECG) and brain (EEG) activity were monitored until the animal was classed as dead. Post the treatment, the internal temperature of the animal was measured by loggers placed into the brain and heart cavity. The electric potential across the brain was also measured. A preliminary evaluation of the EEG and ECG registrations in the individual fish showed that loss of consciousness may occur within 0.5 seconds stun as the fish displays epileptic insult, but unconsciousness could not be verified with EEG. A one-second stun did, however, result in verified unconsciousness both for dry and waterbath stunning. A prolonged electric exposure in combination with a cold brine resulted in permanent loss of consciousness until death, whereas a throat cut or exposure to water supersaturated with CO2 was insufficient and resulted in some fish recovering. Measurements of the electric potential difference across the brain showed that the electric field is dependent on the size of the fish for dry stunning, but not in water. Unconsciousness was reached as low as 2.8 V/cm Vpp across the brain, but with an average of 45 and 14 Vpp for dry and waterbath stunning, respectively. We conclude that electrical stunning in combination with cold brine is effective for humane stunning and killing of lumpfish.Electrical stunning and killing of lumpfish with commercial waterbath and dry stunnerspublishedVersio

Spotted Wolffish Broodstock management and egg production : retrospective, current status, and research priorities

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Effects of altered photoperiod regimes during winter on growth and gonadosomatic index in Arctic charr (Salvelinus alpinus) reared in freshwater

The short- and long-term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2-year-old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.publishedVersio

Physiological effects of recapture and transport from net-cages in lumpfish

Lumpfish are widely used for removing sea lice in salmonid sea-based aquaculture. If these fish are to be harvested and used for human consumption, it is necessary to know how the physical strain associated with removing the lumpfish from the net-cages affects the fish in the short-term, and if live-storage in tanks, well-boats, or nets awaiting slaughter, will result in stress and mortalities. In this study, we investigated the effect of physical stress and mortality in a group of lumpfish recaptured from commercial net-cages, transported to holding tanks, and stored for one week. In addition to cortisol (primary stress response), we analyzed ions directly related to osmoregulation (Na+ and Cl−), osmotic stress (Ca2+), and blood plasma pH as an indicator of a secondary stress response. The aim of the study was to increase the basic physiological understanding of the physiological effects of handling procedures and transport in lumpfish. Only minor, and temporary, effects on primary stress response and secondary stress response were seen in lumpfish recaptured from net-cages and transported to holding facilities, indicating that lumpfish cope well with short transport (here 5 h). These findings are important in a context where lumpfish are harvested for reuse, e.g., human consumption or processing, following their lice-eating stage in net-cages.publishedVersio

Catch me if you can: How to recapture lumpfish using light as an attractant

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Stepwise temperature regulation and its effect on growth, feeding and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.)

To investigate the possible direct effect of a stepwise reduction in temperature with increasing size on growth, feeding parameters and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.), 804 juvenile halibut (mean initial weight individuals: 14.2 g ± 0.2 SEM) were reared at constant 9, 12 and 15 C or shifted (T-step, i.e. 15–12 C after 36 days) for 99 days. Despite indications of lower optimal temperature for growth with increasing size, equal end weights were obtained between the constant 12 C, constant 15 C and T-step groups. Best overall growth was observed for the group kept at constant 12 C. The limited effect of the T-step group may relate to the size at movement (too big), the temperatures investigated (close to optimum) and the time and size interval investigated (too narrow). Differences in growth were reflected more by alterations in feed intake (CT and F%) than by differences in feed conversion efficiencies (FCE). Differences were found with respect to the density of muscle cells, whereas no differences were found between the average muscle cell diameters. The mean diameter of muscle cells tended to increase only slightly with increasing fish weight, while the mean density of muscle cells tended to decrease. Using an optimum temperature of 12 C, an indication of a possible increased rate of hyperplasia in relation to higher growth was seen