The feeding ecology of 0 year-group turbot Scophthalmus maximus and brill Scophthalmus rhombus on Irish west coast nursery grounds

On sandy beach nursery grounds along the west coast of Ireland, 0 year-group turbot Scophthalmus maximus were found to consume six types of crustaceans, in addition to polychaetes. The 0 year-group brill Scophthalmus rhombus fed almost exclusively on mysids, even though nine taxonomic prey groups were identified in the sediment across the investigated beaches. Both species avoided non-motile organisms such as gastropods and bivalves, which were present in high abundances in the sediment and their growth and condition was not significantly related to the quantity or type of prey consumed, temperature or salinity. A high incidence of feeding was detected for both species over the duration of the study, suggesting that food was not limiting on west of Ireland nursery grounds. Temporal partitioning of settlement was detected between S. maximus and S. rhombus, indicating that inter-specific competition for food does not occur between these two flatfish species on west of Ireland nursery grounds.     

Feeding strategy of juvenile (age‐0+ year) Argentine hake Merluccius hubbsi in the Patagonian nursery ground

Age‐0+ year juvenile Argentine hake Merluccius hubbsi (60–150 mm total length, L_T) from San Jorge Gulf, north Patagonian shelf region of the Argentine Sea, had an almost exclusively pelagic diet dominated by the hyperiid amphipod Themisto gaudichaudii and the euphausiid Euphausia lucens. This suggested that final settlement and permanent demersal habitat utilization might not, as previously reported, occur at earlier sizes (c. 20 mm L_T). Their feeding strategy involves specialization at a population level towards both the main pelagic prey, indicating a narrow trophic niche. Novel data are provided which contribute to the growing body of information in relation to the age‐0+ year transitional stage in demersal fishes and particularly to M. hubbsi recruitment in the Argentine Sea.     

Occurrence of age‐0 year dwarf pikeperch Sander lucioperca in late summer – an overlooked phenomenon in reservoirs

Late summer sampling of pelagic age‐0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age‐0 year pikeperch Sander lucioperca (mean 24 mm standard length, L_S, minimum 13 mm L_S) alongside more normal‐sized S. lucioperca that are found at the end of the first growing season (mean 50 mm L_S), resulting in two clearly size‐separated cohorts. Reference to such small age‐0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size‐dependent winter mortality.     

The effect of stocking with 0+ year age‐class Atlantic salmon Salmo salar fry: a case study from the River Bush,Northern Ireland

An enhancement programme based on stocking 0+ year age‐class Atlantic salmon Salmo salar, conducted in the River Bush, Northern Ireland, U.K. over the period 1996–2005, was reviewed with reference to the performance and biological characteristics of wild fish. Wild ova to 0+ year fry (summer) survival was c. 8% with subsequent wild 0+ year fry‐to‐smolt survival c. 9%. Stocked unfed 0+ year juveniles gave c. 1% survival to smolt whilst fed 0+ year S. salar stocked in late summer exhibited survival at c. 5%. Stocking with unfed and fed fry contributed to increased smolt production and helped attain local management objectives between 2001 and 2005. Significant differences in biological characteristics were observed between wild and stocked‐origin fish. Wild‐smolt cohorts were dominated by 2+ year age‐class fish on the River Bush whilst smolts originating from fed fry mostly comprised younger 1+ year individuals. The mean mass of 1+ year smolts derived from stocked fed fry was significantly lower than that of wild 1+ year smolts, although these differences were not evident between older age classes. Differences in run timing between wild smolts and smolts derived from stocked fry were also apparent with the stocked‐origin fish tending to run earlier than wild fish. Although the stocking exercise was useful in terms of maximizing freshwater production, concerns over the quality of stocked‐origin recruits and the long term consequences for productivity are highlighted.     

The influence of the thermal environment and other early life events on growth rate of piglets during lactation

The effects of early life events on average daily weight gain from birth to day 21 (ADG) of suckling pigs kept at different room temperatures (15°C, 20°C and 25°C) from birth to weaning were investigated. Data were collected from litters born by 61 sows in a loose housing system. The ADG for piglets with low birth weight (estimated for birth weights below the 10% percentile) was estimated to be 20 to 30 g higher per day at room temperature 20°C to 25°C compared with 15°C. In contrast, the ADG during the lactation period decreased for larger piglets (estimated for birth weights above the 10% percentile) by 28 g/day at room temperature 25°C compared with 15°C. Thus, high ambient temperatures (20°C to 25°C) are favourable for the growth in smaller piglets during lactation. Neither latency to first suckle nor birth-induced hypoxia, measured as concentration of umbilical cord lactate, affected the growth rate of the piglets. Lowest rectal temperature during the first 24 h after birth had a long-term negative effect on ADG (P<0.05), so that piglets with a lowest rectal temperature of 32.8°C (10% percentile) had an ADG which was on average 19 g lower per day than piglets with a rectal temperature of 37.3°C (90% percentile). Our results showed that hypothermia at birth, low birth weight and high number of suckling piglets lead to reduced ADG during the suckling period. The results suggest that keeping the room temperature at 20°C during lactation to some extent could compensate for the otherwise negative effects of low birth weight on ADG in piglets without decreasing the ADG of high birth weight piglets. However, to avoid hypothermia in the smallest piglets it may be beneficial to increase the room temperature above 20°C during the farrowing period of loose housed sows.