57 research outputs found
The growth of a Welsh strain of Arctic charr Salvelinus alpinus (L.) and investigations into its aquaculture potential
No full textThe growth in captivity of a wild Welsh strain (Llyn Cowlyd) of Arctic charr (Salvelinus alpinus) was compared to that of a commercial Scottish strain over the course of a 12 month experiment. At the conclusion of the study, the Welsh strain had a lower mass and condition factor than the commercial fish, but a similar length. Aspects of the growth and population structure of the Welsh strain imply that it could be a subject for aquaculture development, but such practises will be dependant on further work on selection and broodstock development
The effects of daily ration on growth and smoltification in 0+ and 1+ Atlantic salmon (Salmo salar) parr
No full textThe effects of long-term variations in feed ration were studied during two experiments on Atlantic salmon parr. In the first experiment, three duplicate groups of approximately 500 salmon parr were fed at rates of 100%, 66% or 33% of the manufacturer’s recommendation from shortly after first feeding. Each group were exposed to a photoperiod regime which was expected to result in smoltification 9 months after first feeding. In the second experiment, three duplicate groups of 550 fish were fed 100%, 66% or 33% of the manufacturer’s recommendation from first feeding and exposed to a simulated natural photoperiod, which was expected to result in smoltification 13 months after first feeding. In both experiments fish size increased with ration, with recruitment to the upper modal group (UMG) of the population also related to ration (85-96%, 64-88% and 28-42% UMG fish for the full, two-thirds and one-third ration groups respectively, recorded at the conclusion of each experiment). Throughout each experiment the full and two-thirds ration fish maintained similar whole body lipid concentrations, although lipid concentrations in the one-third ration fish were generally lower. At the conclusion of experiment 1, gill Na+, K+-ATPase activity in UMG fish fed full rations reached 9.5 μmol ADP hydrolysed. mg-1. protein-1. h-1, whereas ATPase activities were lower in the other ration groups. In experiment 2, all groups had similar gill Na+, K+,-ATPase activities at the conclusion of the experiment (6.4-9.3 μmol ADP hydrolysed. mg-1. protein-1. h-1). Following 24h seawater challenges, conducted during the parr-smolt transformation, UMG fish from the full and two-thirds groups of experiment 1 displayed high survival rates (100%) and low serum osmolalities (335 mOsm.kg-1), with lower survival rates (75%) and higher serum osmolalities (370 mOsm.kg-1) recorded in the one-third ration fish. In experiment 2 similar survival rates (100%) and serum osmolalities (350 mOsm.kg-1) were found in all ration groups. It is concluded that under accelerated production regimes, feed restriction may result in underyearling Atlantic salmon smolts developing a poor hypo-osmoregulatory ability. Variations in ration significantly influence growth, although it is believed that growth is dependant on the maintenance of a specific lipid level in the body
Bio-economic costs and benefits of using triploid rainbow trout in aquaculture: Reduced mortality
No full textAnalysis of data collected from rainbow trout farms in the United Kingdom found that mortality levels in triploid rainbow trout were lower than those in diploids. The consequences of rearing triploids, as opposed to diploids, as an intervention to reduce mortality in the U.K. trout farming industry were quantified using a bio-economic model. The model showed that growing triploids could be more profitable than growing diploids, and this was achieved through improvements in productivity (in terms of better survival) and potential for increased product value, and despite the extra costs attributed to purchasing triploid fingerlings
Environmental influences on growth, maturation and smoltification in Atlantic salmon parr, Salmo salar
No full textThe maturation of Atlantic salmon (Safmo safar) parr, and its effects on growth and
smoltification, causes significant economic losses to commercial aquaculture. The
current thesis investigates the role of environmental factors on freshwater
development, with the aim of providing information which would help reduce the
currently observed levels of maturation in farmed salmon.
The effects of short day "winter" photoperiods were investigated by exposing three
replicated groups of fish to an 8 week "winter" photoperiod (LDlO:14) commencing
in May, August or September, in an otherwise continuous light (LD24:0) regime. A
further group was held on LD24:0 throughout. 200 to 300 individuals were PIT
tagged in each group in order to follow the growth of fish undergoing different
developmental strategies, with the retrospective analysis of such development also
possible. The highest incidence of maturation (>20%) was observed in the May winter
photoperiod group, with low levels recorded in the August and September fish «4%),
suggesting that maturation may be influenced during a "critical" period in early
development. Maturation levels were intermediate «9%) in the continuous light
group indicating that seasonally-changing photoperiodic cues are not necessarily
required for gonadal development. The size of mature fish was initially the same as
both immature parr and smolts, although the growth of mature individuals
subsequently declined, and at the conclusion of the experiment they were significantly
smaller. The August photoperiod resulted in the highest incidence of smoltification,
with all other treatments resulting in low levels.
In a second experiment, PIT tagged fish were reared under an 8 or 12 week ''winter''
photoperiod (LD 10: 14) starting in Mayor June, in an otherwise continuous light
(LD24:0) regime. The highest incidence of maturation (> 11 %) was found in the 12
week May fish, with intennediate levels in the 8 week May and 8 week June groups
«8%). Low levels were found within the 12 week June group «0.6%) and it is
suggested that a critical period when maturation is influenced may occur during a
specific, short period in early development. Throughout the experiments, mature
individuals maintained the same size as their immature siblings. The 12 week June
photoperiod appeared to result in the highest level of smoltification, although those
exposed to the 12 week May photoperiod showed the greatest seawater survival.
In both photoperiod experiments, fish showing some signs of smoltification were also
found to be undergoing gonadal development, indicating that maturation and
smoltification are not completely mutually exclusive processes.
Possible nutritional effects were considered using different dietary lipid inclusions
(either 12.5% or 25%) and variable rations of feed (either full, 2/3 or 113 rations).
Different dietary lipid inclusions had no effect on growth, although the whole body fat
content of individuals was affected, with a switch in dietary fat content during
development resulting in a rapid change in body composition. Fish size increased with
ration and, although at the lowest ration of feed whole body fat levels were reduced,
they were maintained at a set level under the high and intennediate rations, implying a
lipostatic control of growth. Maturation levels were low throughout the nutrition
experiments, suggesting that genetic influences may have been important. Dietary
lipid level had a negligible effect on smoltification, although increases in ration
resulted in a greater incidence of smoltification. Using a 0+ photoperiod regime (i.e.
LD24:0 applied from March until December, with the exception of an 8 week period
of LD17:7 applied from August), smolting individuals showed a reduction in smolt
status when compared to those developed under a natural photoperiod. It is suggested
that such regimes restrict the mobilisation of long-tenn energy stores, with the
subsequent development of seawater tolerance affected. However, it was noted that
the 0+ regime had increased the incidence of smolts.
In summary, it has been shown that environmental factors such as photoperiod,
nutrition and temperature can play an important role in the developmental strategies
taken by juvenile Atlantic salmon. Such factors are likely to greatly influence the
attainment of size and/or nutritional thresholds necessary for various developmental
strategies, in particular if such thresholds occur during seasonally-sensitive "critical"
periods when development can be influenced. Furthermore, the life history strategy
undertaken by an individual may be affected by endogenous rhythms, cued by
seasonally-changing environmental factors. However, there are clear indications that
the underlying genetic control of maturation may also be of importance
Biology of daphnia
No full textSwammerdam, the Dutch scientist, was the first author who took notice of any of the Daphniae. In his Historla Insectorum Generalis, 1669, he gave a description of a species of Daphnia, which resembled Daphnia pulex and which he named Pulex arboreus or arborencens. He stated that its beak was slender and pointed, and was used for drawing up food. He called the second antennae arms and described their motion as three-fold—rectilinear, unequal, and gyratory. He asserted that there were two eyes which seemed to be joined together. Merrett mentioned Daphnia in his Pinax rerum Britannicarum, published in 1677
The influence of dietary lipid inclusion and daily ration on growth and smoltification in 1+ Atlantic salmon (Salmo salar) parr
No full textThe effects of diet regime on growth and smoltification in 1+ Atlantic salmon parr were studied. Two groups of approximately 400 salmon parr, in triplicate, were fed diets containing either 25% or 12.5% lipid from first-feeding. Two further treatments were fed either the 25% or 12.5% lipid diet for 98 days, after which they were fed the alternate diet. In a second experiment three groups of 550 parr, in duplicate, were fed at full, two-thirds or one-third of the manufacturers’ recommended ration, from first-feeding. All groups were maintained on their respective diet regimes until smoltification approximately one year after first-feeding. In experiment 1, lipid level had a significant effect on whole body lipid content. However growth and the incidence of smoltification was not affected by dietary lipid inclusion, with upper modal group fish from each treatment achieving a similar smolt status (in terms of condition factor and Na+, K+-ATPase) at seawater transfer. In experiment 2, growth and the incidence of smolt transformation increased with ration. Full and two-thirds ration fish maintained similar body lipid contents throughout the experiment, with that of the one-third ration fish lower only during early development, indicating that growth was controlled by the maintenance of a distinct lipid level. It is concluded that ration, and not dietary lipid inclusion, has a significant effect on growth and the decision to undergo smoltification in salmon parr
A decrease in photoperiod shortly after first feeding influences the development of Atlantic salmon (Salmo salar)
No full textFour groups of Atlantic salmon fry (n=2000) were exposed to continuous light (LD24:0) from first feeding on 18th April 2001, after which they were exposed to either an 8 or 12 week period of short days (LD10:14) starting on either the 21st May or the 18th June. Each group was then returned to LD24:0 until the conclusion of the experiment the following March. In August 200 fish per treatment were individually PIT tagged. All groups were maintained under an ambient temperature regime. The highest levels of sexual maturation in 0+ male parr were recorded in the 12 week/May group (>11% of the entire male and female population), with the lowest levels (6%) in the 8 week/May and 8 week/June groups (
The Hay river limestone, Northwest territories
No full textDuring the latter part of the 1949 field season, the author served as geologist on a California Standard Company field party which was sent to the Northwest Territories to make an examination of the Upper Devonian limestone strata exposed along the Hay river. The objects of this survey were: (1) to further the completion of the California Standard Company's geological map of possible "petroleum bearing formations in northern Alberta and the Northwest Territories, and, (2) to attempt a correlation of the Hay River limestone formation with the petroliferous limestones underlying Leduc, Alberta. The thesis of this paper is a detailed description of the Hay River limestone formation as it is exposed along the Hay river
Applied epidemiology with examples from UK aquaculture
No full textThis paper is a brief introduction to epidemiology and its application to farmed fish health and welfare with examples from the United Kingdom. Epidemiology has the potential to do a great deal more than just identify risk factors. Indeed in many cases useful risk factors cannot be identified due to the complexity of the disease problems and the lack of resources. Epidemiological principles or analytical techniques have been applied in animal welfare studies, and they can reduce the cost of disease monitoring or surveillance and disease control. However, for epidemiological studies to make a real contribution to farmed fish health and welfare it is often necessary to use multidisciplinary teams, obtain good data and coordinate efforts on the major problems
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