Growth Of Juvenile Atlantic Cod Research Articles

The effect of oxygen saturation on the growth and feed conversion of juvenile Atlantic cod (Gadus morhua L.)

In land-based fish farms, water quality can be controlled to support maximum growth and good feed conversion. Oxygen is an important water quality parameter in aquaculture and the objective of this study was to detect the range of oxygen saturations that maximizes growth of juvenile Atlantic cod. The fish (initial body mass 21.9g) were reared at five different levels of oxygen saturation: 65%, 81%, 103%, 121% and 150% of air saturation, for 98days. At oxygen saturation under 100%, the growth of the fish decreased linearly with progressively lower oxygen saturation with the final body mass of fish reared at 65% saturation being 24% lower than that of fish reared at 103% saturation. The final body mass of fish reared at 150% saturation was significantly higher (7%) than that of fish reared at 103% saturation. Feed intake was also affected by oxygen saturation and was proportional to growth while the feed conversion ratio was not significantly affected by oxygen levels. The results suggest that oxygen saturation of at least 100% is required to obtain maximum growth of juvenile Atlantic cod.

Effect of different feeding regimes on growth in juvenile Atlantic cod, Gadus morhua L.

Different feeding regimes (fasting/re-feeding and reduced feeding) were tested in a 131day trial with 1400 juvenile (mean±SE, 132g±1) Atlantic cod (Gadus morhua) in order to see if a compensatory growth response could be elicited, and if hyperplastic growth was stimulated during the compensatory growth phase. The Atlantic cod was fed in compliance with the following five feeding (F) fasting (S) schedules: the control group (Cont) was fed 100% according to a commercial growth table every day, the second group was fed 50% for two weeks and 100% for four weeks (S50), the third group was fed 100% every secondday and 0% the following day (ALT), the fourth group was fasted one week and fed 100% two weeks (S1W), and the last group was starved two weeks and fed 100% four weeks (S2W). At the termination of the experiment, the body mass of the fish in the control, ALT and S50 groups were significantly higher than the fish in S1W and S2W groups. The shorter fasting treatment groups (ALT and S50) consumed significantly less feed (42.9 and 37.5% less feed, respectively) compared to control whereas final weight did not differ between these three groups. Growth rate was highest in the S50 group (0.78%day−1), and lowest in the longer fasting period groups (S1W, 0.59%day−1 and S2W, 0.57%day−1). White muscle fibre diameter, white muscle fibre density and the percentage of small fibres below 25μm was measured in the control and S2W group and did not differ at any sample point during the experiment. There were minor differences between the groups in percentage distribution of fibre diameter classes. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days or by periodically fasting and re-feeding juvenile cod.

Growth in juvenile Atlantic cod ( Gadus morhua L.) fed continuously or during light or dark hours

This study aimed to investigate the effect of different feeding regime in relation to constant light regime on growth and feed intake among juvenile Atlantic cod. Three experimental groups (duplicated) were held under LD12:12 photo period and constant water temperature (12 °C) for six months. All groups were fed daily in excess using three different regimes: fed continuously (control group, DL), fed during light hours (L) or fed during dark hours (D). From an initial weight of 5 g, average body wet weight at the end of the trial in the D group (95 g) compared to L fish (88 g), whereas DL group took an intermediate position (91 g). No significant differences were observed between the groups at either time. The D group appeared to have higher feed conversion efficiency compared to the other groups, although there were no significant differences between the groups.

Interaction between temperature and photoperiod on growth and feeding of Atlantic cod (Gadus morhua): possible secondary effects

Interactions between temperature and photoperiod on growth of Atlantic cod (Gadus morhua) juveniles (initial weight 9.1 g) were studied by rearing juvenile cod 3 months under simulated natural photoperiod (LDN) and continuous light (LD24:0) at 7, 10, and 13 °C. Juvenile Atlantic cod exposed to LD24:0 had higher growth rate and better feed conversion efficiency compared with cod reared under LDN. Optimal temperature for growth of juvenile Atlantic cod in the size range 5–50 g was influenced by photoperiod and was estimated to be 12.3 °C under LD24:0 and 15.7 °C under LDN. After termination of the laboratory study, the fish were reared in sea pens at ambient conditions for 17 months. The growth-enhancing effect of LD24:0 could be traced far beyond the duration of the laboratory trial, as the final mean weights in June 2005 of the fish reared at LD24:0 and 13 and 10 °C in the laboratory trial were 8% and 13% higher than those of the respective LDN groups. Our study indicates a physiological mechanism that might be linked to cod migrations, as maximal growth and feeding efficiency will be attained in areas during a season with extended day length or continuous light.

Effects of chronic nitrite exposure on growth in juvenile Atlantic cod, Gadus morhua

The effects of nitrite concentration on growth and feed intake in juvenile cod, Gadus morhua, were examined. In the experiment, juvenile cod with a mean (S.D.) live weight of 7.0 (1.9) g were exposed to four concentrations of nitrite [0, (control), 1.0 (low), 2.5 (medium) and 5 mg NO 2–N l − 1 (high)] for 96 days at 8.0 °C, salinity 33 ppt and pH 8.0. No mortality occurred in any of the experimental groups throughout the study. Growth was significantly reduced in fish exposed to all treatment levels, with reduced growth in the high concentration group in the first period of the experiment (day 1–31) and in all experimental concentrations during later periods. No significant difference in feed intake or food conversion efficiency was observed between treatment groups. The fish from the exposed groups displayed an acclimatory response to nitrite. These results indicate that management of intensive aquaculture systems of G. morhua, should avoid levels of nitrite even at 1.0 mg NO 2–N l − 1 not to impair growth.

The interrelation between temperature regimes and fish size in juvenile Atlantic cod (Gadus morhua): effects on growth and feed conversion efficiency

The present paper describes the growth properties of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C, and a group reared under “temperature steps” i.e. with temperature reduced successively from 16 to 13 and 10 °C. Growth rate and feed conversion efficiency of juvenile Atlantic cod were significantly influenced by the interaction of temperature and fish size. Overall growth was highest in the 13 °C and the T-step groups but for different reasons, as the fish at 13 °C had 10% higher overall feeding intake compared to the T-step group, whereas the T-step had 8% higher feeding efficiency. After termination of the laboratory study the fish were reared in sea pens at ambient conditions for 17 months. The groups performed differently when reared at ambient conditions in the sea as the T-step group was 11.6, 11.5, 5.3 and 7.5% larger than 7, 10, 13 and 16 °C, respectively in June 2005. Optimal temperature for growth and feed conversion efficiency decreased with size, indicating an ontogenetic reduction in optimum temperature for growth with increasing size. The results suggest an optimum temperature for growth of juvenile Atlantic cod in the size range 5–50 g dropping from 14.7 °C for 5–10 g juvenile to 12.4 °C for 40–50 g juvenile. Moreover, a broader parabolic regression curve between growth, feed conversion efficiency and temperature as size increases, indicate increased temperature tolerance with size. The study confirms that juvenile cod exhibits ontogenetic variation in temperature optimum, which might partly explain different spatial distribution of juvenile and adult cod in ocean waters. Our study also indicates a physiological mechanism that might be linked to cod migrations as cod may maximize their feeding efficiency by active thermoregulation.

Effect of chronic ammonia exposure on growth in juvenile Atlantic cod

The effects of chronic un-ionised ammonia (UIA-N) exposure on growth and food conversion efficiency in juvenile Atlantic cod, Gadus morhua, were examined. Fish with a mean (SD) initial weight 16.7 (3.4) g were exposed to four concentrations of UIA-N, ranging from 0.0005 mg l −1 (control) to 0.17 mg l −1, for 96 days at 13 °C. Compared to the control, growth was significantly reduced at UIA-N concentrations above 0.06 mg l −1, but the fish experiencing the most severe UIA-N concentrations still maintained high growth rates (>1% day −1). The growth reduction is attributed to a decrease in food intake. Fish from the exposed groups displayed an acclimatory response to UIA-N, as growth rate reduction in these groups, compared to the control, diminished as the experiment progressed, and in the last period, growth rates in the UIA-N exposed groups were not significantly different from that of the control. Concurrently, a reduction in plasma urea-N content was seen in these groups at the end of the experiment, indicating an increased efflux of urea in response to high ambient UIA-N.