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

Effects of chronic and periodic exposure to ammonia on growth and blood physiology in juvenile turbot (Scophthalmus maximus)

Juvenile turbot (Scophthalmus maximus) were exposed periodically and chronically to different levels of un-ionised ammonia (UIA-N) and the subsequent effect on growth and food conversion efficiency was studied. Fish with a mean (SD) initial weight 19.3 (3.9) g, were exposed to five treatments consisting of a control group, two groups (ChronicLow and ChronicHigh, UIA-N levels of 0.13 and 0.25 mg l- 1, respectively) chronically exposed to ammonia and two groups (LowPulse and HighPulse) exposed to the same levels as above for a short period daily. The fish were held for 64 days at 18 °C, a pH of 8.04 and a salinity of 33.5‰. At the end of the experiment, fish from the Control group had a significantly higher mean weight (95.5 g) compared to all other groups. Fish from the ChronicHigh group displayed the lowest mean weight (74.6 g), whereas fish in the ChronicLow, LowPulse and HighPulse groups displayed mean weights of: 79.3 g, 82.8 g and 81.9 g, respectively. Blood ion concentrations were not affected significantly in any of the treatments, whereas minor reductions in blood pH, partial pressure of CO2 and total CO2 content were found in ammonia exposed groups up until day 44 of the experiment. Feed conversion efficiency, daily feeding rate and total feed consumption did not vary significantly between treatments. The study demonstrate that short daily ammonia peaks may result in negative effects on growth, equivalent to that found under chronic ammonia exposure in juvenile turbot

Interactive effects of oxygen saturation and ammonia on growth and blood physiology in juvenile turbot

The effects of dissolved oxygen concentration combined with sublethal doses of un-ionised ammonia nitrogen (UIA-N) on growth and physiology were investigated in juvenile turbot. Fish with a mean ± SD initial weight of 19.1 ± 4.1 g, were reared in replicate at normoxic (80¿85% O2 saturation) and hyperoxic (110¿115% O2 saturation) conditions, combined with either control or two sublethal concentrations of un-ionised ammonia (0, 0.17 and 0.31 mg UIA-N l¿ 1) added for 64 days at 18 °C and pH 8.04 in a flow-through system. The subsequent effect of fixed O2 and UIA concentrations on growth and blood physiology was measured every 22 days. The results show that UIA-N concentrations only had a negative effect on growth under normoxic conditions, suggesting that hyperoxic conditions may increase tolerance to un-ionised ammonia in juvenile turbot. Only minor effects on the acid-base balance were found. A generally higher blood CO2 and PCO2, along with an accumulation of HCO3¿ resulting in an increased blood pH was found in the hyperoxic groups towards the end of the experiment. We conclude that, under normoxic conditions, a chronic exposure of ammonia above 0.17 mg UIA-N l¿ 1 will have a negative effect on growth and that hyper-oxygenation can be a possible solution to counteract this harmful effect

Improving growth in juvenile turbot (Scophthalmus maximus Rafinesque) by rearing fish in switched temperature regimes

The effect of thermal history (16 and 20°C) on growth of juvenile turbot, Scophthalmus maximus (initial mean weight 72.6 g, n = 157) was studied. Fish were divided into four groups, two groups remaining at constant temperature (C16, C20), while fish in the other groups were transferred from either 16 to 20°C (F16-20) or from 20 to 16°C (F20-16). Between 35 and 42 fish in each tank were individually tagged at the start of the experiment. The final mean weights were significantly higher in the F20-16 group (230 g) than in the C20 (213 g), F16-20 (211 g) and C16 (205 g) groups. The overall growth rate was highest in the F20-16 group (1.17% day¿1) but comparable in the three other groups (1.00¿1.04% day¿1). Our findings indicate that, even at near-optimal temperature for a given size, the temperature history of the fish may influence future growth. Based on these indications, we conclude that as turbot grow larger, the temperature should be reduced to take advantage of the change in optimal temperature for growth with increasing fish size rather than rearing at constant temperatures

Commercial-scale validation of temperature-step rearing on growth physiology in turbot, Scophthalmus maximus

The aim of this study was to investigate the possible benefit of "temperature-steps" (T-steps) rearing for juvenile turbot (initial weight 15.1 g) under realistic production scale and to determine whether initial growth advantage is maintained throughout the rearing period to market size. One group (called T-step 22-19-16) of juvenile turbot was reared at three different temperatures, that is, 22 C (from 17 to 60 g) followed by 19 C (from 60 to 100 g) and 16 C (>100 g); another group (called T-step 19-16) at two temperatures, that is, 19 C (from 17 to 100 g) and lowered to 16 C (>100 g); and the third group (called C16) at one constant temperature, that is, 16 C. Relative growth was significantly higher in the two T-step groups, with the T-step 19-16 showing the highest overall growth. Feed conversion efficiency was highest in the 19-16 group. Only minor effects of the experimental rearing on blood physiology were found, with one notable exception of inverse relationship between plasma glucose and growth. Overall, these findings indicate that a short interval of rearing fish at high temperature during the early juvenile phase may have a long-term effect on biomass increment in turbot. This is an important finding for the turbot industry