Terje Refstie

The effect of fish density and feeding regimes on individual growth rate and mortality in rainbow trout (Oncorhynchus mykiss)

Abstract Feeding frequency and fish density were varied in a 3 2 matrix rearing experiment with rainbow trout of initial size between 130 and 250 mm fork length. All fish groups were given similar daily rations. Initial densities were 107–219 kg m −3 and final densities 240–450 kg m −3 . The parameters of daily fork length increase, specific growth rate and mortality were recorded. Mean individual growth rate, irrespective of feeding regime, was highest in the lowest density and lowest in the highest density. Growth rate increased with increased feed availability. High feed availability (high frequency of feeding) was especially important when densities were extremely high.

Selection experiments with salmon: III. Genetic and environmental sources of variation in length and weight of Atlantic salmon in the freshwater phase

Abstract Atlantic salmon ( Salmo salar ) brood stock were taken from 32 strains in Norway for 3 consecutive years. Each year, after fertilization, the offspring in each family from each strain were reared in separate egg trays and fingerling tanks. Individual weights and lengths were recorded on a sample of fish from each tank. Environmental and genetic factors influencing the growth rate were studied. The length and weight at a standardized age were significantly affected by hatching date and number of fish held in a tank. There was also a significant ‘tank effect’ which influenced the heritabilities estimated. Significant differences between strains were found for all three year-classes ( P

Effect of density on growth and survival of rainbow trout

Abstract Groups of rainbow trout ( Salmo gairdneri ) were kept at five different densities during an initial feeding period of 42 days and a subsequent growth period of 180 days. They were then kept at the same density for 55 days. Differences between groups in mean weights and mortality were found as early as the end of the initial feeding period. At the end of the 180-days growth period the differences in mean weight between density groups were large. Differences in condition ( K ) factor were also found at the end of this period. Groups at high densities had the lowest growth rate and K factor. When groups were kept at the same density, those originally at high densities showed the highest relative growth. It is concluded that high densities depressed the growth rate, and that compensatory growth occurred when the densities were standardized. It is important to take density into account when ranking families or progeny groups for growth performance.

Effect of density on growth and survival of artificially reared Atlantic salmon

Abstract Groups of salmon ( Salmo salar ) from two localities were kept at five different densities during the initial feeding period of 42 days and a subsequent growth period of 205 days. They were then kept at the same density for 95 days. Differences in mean weight between fish from different localities were found as early as the end of the initial feeding period. No marked differences were found between mean weights of fish held at different densities during the initial feeding period, while the mortality rate of fry decreased with higher densities for both strains. At the end of the 205-day growth period the differences in mean weight between strains and between density groups within a strain were large. Significant interaction between locality and density was also found. Part of this interaction is due to scale effects. When groups were kept at the same density, those originally at high densities showed the highest relative growth, and also had the highest K -factor at the end of this period. It is concluded that high densities depressed the growth rate, and that compensatory growth occurred when the densities were standardized. It is important to take density into account when ranking families or progeny groups for growth performance in selective breeding trials.

Effect of varying dietary protein level in different families of rainbow trout

Groups of rainbow trout (Salmo gairdneri) fingerlings from five different families and five inbred groups were fed for 153 days on each of four diets similar in energy content, but differing in their percentage of protein. The protein contents were 24, 33, 42 and 51%, respectively. Significant differences between fish families were found for growth, condition factor, chemical composition of the carcass, and digestibility of protein. At the end of the experiment, interaction between diet fed and family was found close to significance for weight and relative growth rate, and significant for length and condition factor. This interaction indicates that prospects for selectively breeding strains of rainbow trout specifically better able to utilize protein are promising. Fish growth rate increased with increasing dietary protein content. The corresponding condition factor, content of dry matter and energy in the carcass decreased. The high protein diets gave more protein in the carcass and a more discoloured liver than the low protein diets. Apparent protein digestibility increased with increasing protein level.

Induction of polyploidy in salmonids by cytochalasin B

Abstract The purpose of this study was to investigate the possibility of producing tetraploid fishes. Eggs of salmon (Salmo Salar) and rainbow trout (Salmo gairdneri) were treated with concentrations of cytochalasin B ranging from 1 μg/ml to 100 μg/ml for varying periods of time. All treated groups had higher death rates than untreated controls. If the treatment was started immediately after fertilization and before the eggs had swollen all eggs died. The highest frequency of mosaic embryos and polyploid cells was obtained when the treatment started 35–70 h° (hour-degrees) after fertilization and lasted until about the 4-cell stage of development. A dose of 10 μg/ml of cytochalasin B gave the most satisfactory results. This concentration was used for further work. Two batches of 6000 salmon eggs and several groups of rainbow trout eggs were treated and hatched. The hatchability was generally low while the control group had a normal hatchability. If some of the treated fish are eventually found to be tetraploids and fertile, they will be used to produce triploid offspring by crossing with normal diploid fish.

Complete diallel cross between five strains of Atlantic salmon

Abstract The effect of cross-breeding on survival, growth and maturity when crossing five Norwegian strains of Atlantic salmon has been investigated. A diallel cross including purebred strains and their reciprocal crosses was used. Additive, maternal and heterosis effects were studied. Total heterosis was partitioned into average, general and specific heterosis. Growth of maturing and immature males and females was also considered. Significant total heterosis was found for survival of fry, survival of fish after marking (marked at one year of age), body weight of fingerlings and body weight of adults. However, average heterosis was low for all traits. For survival of eyed-eggs, alevins and fingerlings, dressing percentage and maturity, total heterosis was not significantly different from zero. It is concluded that cross-breeding Norwegian strains of Atlantic salmon seems to have little practical significance in a future breeding program.

A genetic analysis of egg, alevin and fry mortality in salmon (Salmo salar), sea trout (Salmo trutta) and rainbow trout (Salmo gairdneri)

Abstract Heritability of mortality in eggs, alevins and fry were estimated using data from salmon, sea trout and rainbow trout. The highest value (average for all species and both estimation methods) based on the sire component was obtained for the eyed egg stage, h 2 = 0.08, followed by the alevin stage, h 2 = 0.05, while estimates for fry mortality did not differ significantly from zero. The maternal effect was rather large for uneyed eggs and eyed eggs, while it was low for alevin mortality. Maternal effects were also found to have a significant influence on the mortality of salmon fry. It was, however, not possible to separate maternal effects from tank effects.

Hybrids between Salmonidae species. Hatchability and growth rate in the freshwater period

Abstract In 1972 a hybridization experiment with salmonids was initiated at the Fish Breeding Experimental Station, Sunndalsora. The purpose of this experiment was to study the viability, performance traits and the fertility of hybrids. Hybrids were produced from the following members of the salmon family: Salmon (Salmo salar), sea trout (Salmo trutta), brown trout (Salmo trutta), rainbow trout (Salmo gairdneri) and arctic char (Salvelinus alpinus). All crosses attempted, except those involving the rainbow trout, were relatively successful. Considerable differences in the hatching rates of the different hybrids were observed. All crosses with the arctic char were heavier than the better pure bred specimens at 11 months. In all other crosses the hybrids were lighter than the purebred specimens. The experiment is continuing, it is evident that more research is necessary before the potential value of these hybrids for fish farming can be properly assessed.

Genetic and environmental sources of variation in body weight and length of rainbow trout fingerlings

Abstract Environmental and genetic factors influencing the growth rate of rainbow trout were studied. Body weight and length at a standard age were significantly affected by first-feeding date and number of fish held in a tank. The estimates of heritabilities found for different year-classes varied. The heritabilities estimated from the total data after adjustment for first-feeding date and density were 0.06 for weight and 0.20 for length using the sire components of variance. Calculated from the dam components, the heritabilities were 1.04 for weight and 0.63 for length. The genetic and phenotypic correlations between length and weight estimated from the total data were 1.02 and 0.93, respectively.