The role of dietary methionine concentrations on growth,metabolism and N‐retention in cobia (Rachycentron canadum) at elevated water temperatures

This study determined impacts of dietary methionine concentrations at two temperatures on growth, feeding efficiency and N‐metabolites in juvenile cobia. Methionine concentrations of the experimental diets were deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg). Water temperature was normal (30°C) or elevated (34°C). Twenty cobia in triplicate tanks were fed the experimental diets for 6 weeks. Both methionine and temperature affected cobia's growth and feeding efficiency. Cobia fed M9 performed lower than the fish fed M12 and M16 diets. Additionally, cobia reared at 34°C performed poorer than at 30°C, probably due to lower voluntary feed intake in the fish reared at 34°C. Protein efficiency ratio and protein productive value in cobia fed M9 diet were less than M12 or M16 diets. This was confirmed with the improved retentions of indispensable amino acids (AAs). No interactions between methionine and temperature were observed in growth and protein accretion. At 30°C, CF improved, while HSI and VSI declined upon methionine supplementation levels. Of which an interaction between temperature and methionine was present. Plasma, muscle and liver free AA and N‐metabolites were affected by methionine and temperature. Furthermore, temperature affected cobia's lipid class composition, resulting in increased phospholipids and cholesterol at 34°C.     

Effects of temperature on growth and fatty acid synthesis in the cyclopoid copepod <Emphasis Type="Italic">Paracyclopina nana</Emphasis>

We have used the cyclopoid copepod Paracyclopina nana to understand responses to the temperature shift. To determine the changes of molecular mechanisms, which would lead to physiological changes in P. nana, we investigated mRNA expression involved in lipogenesis, the area of lipid droplets, the ratio of fatty acids, and life parameters (growth and fecundity) in response to temperature changes (15, 20, and 30 °C) with comparative control at 25 °C. Setting the temperature 25 °C as a standard point, there were increases in mRNA expression, the area of the lipid droplets, and fatty acid composition at temperatures below the standard (15 °C), while all the markers mentioned above significantly decreased at higher temperatures than the standard (25 °C). Through fecundity and growth rate experiments, daily nauplii production was reduced and growth retardation was observed at both 15 and 20 °C, but no noticeable differences in the two parameters were observed at 30 °C compared to the control (25 °C). This study provides a better understanding of the effects of temperature on lipogenesis in copepods.     

Effects of high carbohydrate and high lipid diets on growth,body composition and glucose metabolism in southern catfish at two temperatures

The effects of high carbohydrate and high lipid diets on the growth, body composition and glucose metabolism in the southern catfish were determined at 17.5 °C and 27.5 °C. At each temperature, the feeding rate, specific growth rate and protein productive value decreased with increasing dietary carbohydrate (P<0.05). Feed efficiency and protein efficiency ratio were lower in the fish fed a high dietary carbohydrate diet at 17.5 °C, but were not significantly different between diets at 27.5 °C. Plasma glucose and activities of pyruvate kinase and glucose‐6‐phosphate dehydrogenase were higher in fish reared at 27.5 °C than those reared at 17.5 °C, and within each temperature, they were higher in fish fed the high‐carbohydrate diet. Hepatosomatic index was higher in fish fed the high‐carbohydrate diet than those fed the high‐lipid diet at 27.5 °C, but no significant difference was found at 17.5 °C. The results indicate that higher temperatures enhance glycogen deposition and lipogenous enzyme activities when fed with a high‐carbohydrate diet; thus, at higher temperatures, this fish uses carbohydrate more efficiently for protein sparing.     

Effect of temperature on growth performance of greater amberjack (SERIOLA DUMERILI Risso 1810) Juveniles

In order to successfully diversify Mediterranean aquaculture, it is necessary to determine optimum culture conditions of potential candidate species such as greater amberjack (Seriola dumerili). Among culture conditions, rearing temperature is a key factor for achieving optimum growth and maintaining fish welfare. However, little is known about the optimum culture conditions of greater amberjack (Seriola dumerili). Thus, the aim of this study was to determine the effect of three different rearing temperatures (17, 22 and 26°C) during 120 days on growth performance, body morphometry, biochemical composition, gut transit and liver morphology of greater amberjack (Seriola dumerili) juveniles. After 120 days of rearing, fish raised at 26°C showed higher (p < .05) body weight and specific growth rate than fish held at lower temperatures, as well as improved feed utilization, protein efficiency and nutrient retention percentages. Fish stomach emptying was faster (p < .05) in fish raised at 26°C than in fish held at 22°C and 17°C. Similar results were obtained for gut transit time, being gut emptying faster (p < .05) in fish reared at 26°C than in fish cultured at lower temperatures. Rearing temperature also induced changes in fish morphology which resulted in a higher (p < .05) caudal propulsion efficiency index for fish reared at 26°C. Based on these results, we conclude that greater amberjack fingerlings perform better at 26°C than at 22°C or 17°C.     

Effects of temperature on growth, survival and body composition in larvae of barbel, Barbus barbus (L.)

Barbel larvae were reared for 21 days at 21.0, 24.1, 27.2 or 30.0 °C and fed ad libitum live Artemia nauplii for 16 h a day. The final survival rates exceeded 99 %. The highest mean daily growth rates, amounting to 0.97 mm total length (TL) and 17.3 % body weight (BW), were found at 27.2 °C. The optimum temperature calculated for the growth of larvae was 26.9 °C for TL and 26.5 °C for BW. An increase in water temperature accelerated the development rate to a larger degree than the growth rate. Temperature significantly influenced the final fish body chemical composition. The lowest dry matter content (19.1 %) was found at 24.1 °C. The highest values of ash content were determined for 27.2 and 30.0 °C and were 11.3 and 11.0 % of dry matter, respectively. The fish body caloric value was the highest at 30.0 °C (30.0 J mg^?1). The analysis of changes in the fish body chemical features against the effective day-degrees age scale did not reveal significant influence of temperature. Therefore, the effects of temperature on larval body composition seem to be related mainly to differences in barbel developmental progress at particular temperatures.     

Effect of water temperature on energy budget of Nile tilapia,Oreochromis niloticus

A 21‐day growth trial was undertaken to investigate the effect of water temperature (25, 28, 31, 34, 37 °C) on growth, feed utilization and energy budget of juvenile Nile tilapia (Oreochromis niloticus) (initial body weight around 12 g) with four replicates at each temperature. Feed intake energy (IE), recovered energy (RE), faecal energy (FE), excretory energy (UE + ZE) and heat energy (HE) were calculated to obtain the energy budget. The results showed that feeding rate and ammonia excretion were not significantly affected by water temperature. Specific growth rate in wet weight (SGRw) and FE was significantly lower in the fish reared at 37 °C while no significant difference was observed between the fish reared at 25–34 °C. Protein retention efficiency was highest at 28 °C and lowest at 37 °C. The proportion of IE channelled into RE and UE + ZE was lower while those lost in HE was higher in the fish reared at 37 °C. The optimal growth temperature was estimated as 30.1 °C based on the regression of SGR and water temperature. Energy budget at maximum growth (34 °C) was: 100 IE = 27.0 RE + 1.1 (ZE + UE) + 10.6 FE + 59.2 HE. HE accounted for 69.3% and RE for 30.7% of metabolizable energy.     

Influence of lipid level and supplemental lecithin in diet on growth,feed utilization and body composition of juvenile flounder (Paralichthys olivaceus) in suboptimal water temperatures

This study was conducted to investigate the influence of dietary lipid level and supplemental soy lecithin on growth, feed utilization and body composition of juvenile flounder reared at two suboptimal water temperatures, 12 and 17 °C. Three isonitrogenous (CP 50%) diets containing 1% squid liver oil (S7), 7% squid liver oil (S14), and a mixture of 2% soy lecithin and 5% squid liver oil (SL14) were formulated to obtain 7% and 14% of crude lipid. Triplicate groups of fish (6.3 ± 0.2 g) were fed to apparent satiation twice a day for 60 days. Weight gain, daily feed intake, feed efficiency and protein efficiency ratio were significantly higher for fish reared at 17 °C than at 12 °C. Daily feed intake was significantly decreased with the increase of dietary lipid level at the same water temperature, but weight gain was not affected by dietary lipid composition. At 12 °C, feed efficiency and protein efficiency ratio were significantly higher for fish fed the S14 and SL14 diets than those of fish fed the S7 diet, while at 17 °C feed efficiency and protein efficiency ratio of fish fed the S14 diet, which were not significantly different from those of fish fed the SL14 diet, were significantly higher than those of fish fed the S7 diet. There were no significant effects of dietary lipid composition or temperature range on the whole body contents of moisture, crude protein, lipid or ash. Dietary lipid composition and temperature affected the fatty acid content of the polar lipid from the liver; and the n-3HUFA contents such as 20:5n-3 and 20:6n-3 were higher at 12 °C than at 17 °C. The results of this study indicate that an increase of dietary lipid level from 7% to 14% has beneficial effects on feed utilization of flounder when reared in suboptimal water temperatures. The increase of water temperature from 12 to 17 °C improved growth and feed utilization, but 2% soy lecithin had no substantial effect on growth and feed efficiency of juvenile flounder.     

Influence of temperature and feeding regimes on growth and notochord deformity in reared <Emphasis Type="Italic">Anguilla japonica</Emphasis> leptocephali

The high mortality rate of reared Japanese eel Anguilla japonica larvae is largely due to lower growth rate and the higher rate of deformed larvae. To establish an effective rearing protocol for this species, we examined the effects of water temperature and feeding regimes on their growth and notochord kyphosis. Larvae at 165 days post hatching were reared for 28 days at mean temperatures of 24, 25 and 27 °C, and were fed 4 or 6 times per day. Larval growth rate was significantly higher in larvae reared at 24–25 °C and fed 6 times per day. However, growth rate was significantly reduced at 27 °C, suggesting a shortage of metabolic energy due to an elevated cost of the higher basal metabolic rate at higher temperatures and low nutritional performance of currently used artificial diet. Notochord kyphosis was promoted by elevated water temperature, and two-way ANOVA showed that water temperature and feeding frequency had combined effects on the deformity. These findings suggest the importance of concurrently manipulating both environmental and nutritional factors to produce healthy eel larvae in captivity.     

The effect of low temperatures and photoperiods on growth and vertebra morphometry in Atlantic salmon

The aim of this study was to reveal possible interactive effects of temperature and photoperiod on somatic and skeletal growth, feed conversion, organ indexes and blood chemistry in Atlantic salmon postsmolts. A total of 1140 (initial mean weight 96.0 g ± 3.1 SEM) juvenile Atlantic salmon reared in seawater were in duplicates exposed to six different combinations of temperatures (4.3, 6.5 or 9.3 °C) and photoperiods (continuous light, LL or simulated natural photoperiod (69ºN), LDN) for 124 days. An interactive effect of photoperiod and temperature on somatic growth was found as the fish exposed to low temperature and continuous light regime (4LL) had a significantly higher growth (30 % gain in overall SGR) than the 4LDN group, corresponding to the effect of approx. 1.2 °C temperature increase. Fish in the 6 and 9 °C groups did not show any significant growth benefit of continuous light. Compared to the 4LDN group, the 4LL group showed higher total feed conversion efficiency, lower levels of blood Na⁺ and lower hepato-somatic and cardio-somatic indexes. In the skeleton, cervical vertebra were largest in the 4LL group, while the length of the head was largest in the 4LDN group, continuous light promotes growth at lower temperatures while supporting a normal development. It is suggested that a considerable growth benefit may be achieved by exposing juvenile Atlantic salmon to continuous light when reared at low (in this trial 4.3 °C) water temperature during winter.     

Effects of water temperature on feeding and growth of juvenile marbled flounder <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis> under laboratory conditions: evaluation by group- and individual-based methods

To determine the optimal temperature for juvenile (0 year old) marbled flounder Pseudopleuronectes yokohamae, juveniles of 40–54 mm standard length were reared at six temperature conditions in the range of 8–26 °C, using group- and individual-based methods. Growth of juveniles increased from 8 to 20 °C but decreased from 20 to 26 °C, irrespective of the rearing method used. Food intake was greatest at 20 and 24 °C compared with other temperatures, while feed conversion efficiency was greater at 20 °C than 24 °C in individual rearing. Individual rearing provided more information such as individual variations in growth and food consumption, suggesting the importance of individual-based experiments for exploring the optimal temperature for fish.     

Choice preference of diets with different protein levels depending on water temperature in Nile tilapia

This study tested a choice feeding model for Nile tilapia that allowed the selection of a higher or lower protein content in the diet depending on water temperature. Nile tilapia were reared in twelve 200-L tanks for 63 days with 12 fish (body weight 38 g/fish at start) per tank. Two temperatures (22 or 30°C) and two color combinations (yellow and red each) for a two-component diet containing 30% (low) and a 38% (high) crude protein content based on dry matter were used. High water temperature (30 vs. 22°C) resulted in a significantly higher feed rate (1.93 ± 0.123 and 1.26 ± 0.100%, respectively), body weight gain (39.3 ± 4.29 and 4.75 ± 0.66 g, respectively), final body weight (70.3 ± 9.31 and 43.0 ± 7.49 g, respectively), and feed efficiency (55.4 ± 6.09 and 14.6 ± 2.86%, respectively), as well as protein efficiency ratio (1.687 ± 0.186 and 0.450 ± 0.087, respectively), regardless of color codes. No significant differences of color codes on growth parameters, body composition, and fatty acid profile were seen. Higher water temperature (30 vs. 22°C) only had an effect on percentage-specific fatty acids of total fatty acids of the whole body (biggest difference: C16:0, 20.5 ± 1.00 and 17.4 ± 1.11%, respectively). Therefore, water temperature clearly influences growth and fatty acid composition of the body.     

Effect of temperature and salinity on virulence of Edwardsiella tarda to Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel)

Experiments were designed to determine the effects of temperature and salinity on the virulence of Edwardsiella tarda to Japanese flounder, Paralichthys olivaceus. In the temperature experiment, a two‐factor design was conducted to evaluate the effects of both pathogen incubation temperature and fish cultivation temperature on pathogen virulence. E. tarda was incubated at 15, 20, 25 and 30±1°C, and the fish (mean weight: 10 g) were reared at 15, 20 and 25±1°C respectively. The fish reared at different temperatures were infected with the E. tarda incubated at different temperatures. The results of a 4‐day LD₅₀ test showed that temperature significantly affected the virulence of E. tarda (P<0.01) and the interaction between the two factors was also significant (P<0.01). For fish reared at 15°C the virulence of E. tarda was the highest at 25°C of pathogen incubation, followed by 20, 15 and 30°C. When the fish rearing temperature was raised to 20 and 25°C, the virulence of E. tarda incubated at all temperatures increased. Isolation testing demonstrated results similar to those of LD₅₀. The higher rearing temperature increased the proliferation rate of the pathogen in fish. In the salinity experiment, the incubation salinity of E. tarda was at 0, 10, 20 and 30 g L^?1, respectively, and the fish with mean weight of 50 g were cultured in natural seawater of 30 g L^?1. The results of one‐way anova in 4‐day LD₅₀ test showed that incubation salinity significantly affected virulence. Virulence was lower when the salinity of the incubation medium was at 0 and 30 g L^?1, higher at 10 and 20 g L^?1. The results of isolation test were in accordance with those of LD₅₀. At 20 g L^?1E. tarda had a faster proliferation rate than that at 10 g L^?1.     

Effect of temperature and dietary protein/lipid ratio on growth performance and nutrient utilization of juvenile Senegalese sole (Solea senegalensis)

A 74‐day trial was undertaken to evaluate the effects of temperature (16 and 22 °C) and dietary protein/lipid ratio on the performance of juvenile Senegalese sole (mean body weight: 6.4 g). Four experimental diets were formulated to contain two protein levels (550 g kg^?1 and 450 g kg^?1) combined with two lipid levels (80 g kg^?1 and 160 g kg^?1). Growth was higher at 22 °C and within each temperature in fish fed diets 55P8L and 45P16L. Feed efficiency, N retention (% NI) and energy retention (% EI) were higher at 22 and at both temperatures in fish fed diet 55P8L. Temperature affected whole‐body composition, with dry matter, protein, lipid and energy being higher and ash lower in fish kept at higher temperature. Independently of temperature, whole‐body lipid, energy and ash were higher and protein was lower in fish fed the high‐lipid diets. Visceral and hepatosomatic indices were not affected by diet composition but were higher in fish kept at 16 °C. Liver glycogen and lipid contents and activities of glutamate dehydrogenase, alanine and aspartate aminotransferases were not affected by diet or water temperature. Malic enzyme (ME) and glucose 6‐phosphate dehydrogenase activities were higher in fish fed the low‐lipid diets. ME activity was higher at lower temperature. In conclusion, increasing water temperature from 16 to 22 °C improves growth and feed efficiency of Senegalese sole juveniles; regardless of water temperature, the diet with 550 g kg^?1 protein and 80 g kg^?1 lipid promoted the best growth and feed efficiency.     

Influence of temperature on yolk resorption in common snook Centropomus undecimalis (Bloch, 1792) larvae

To determine the optimal rearing temperature for Centropomus undecimalis larvae during the yolk resorption period, changes in larval development were measured at four different temperatures (23, 25, 28 and 31°C). Yolk and oil‐globule volume was recorded for 25 larvae at four different times. This involved an initial measurement at hatch and at 24, 48 and 72 h posthatch (hph). Additional morphological measurements included standard length, body height and eye diameter. On average, at the end of the three trials, larvae reared at 25°C had a longer mean standard length than larvae reared at 23, 28 and 31°C. Larvae reared at 25°C also had more yolk and oil globule reserves than larvae raised at 28 and 31°C. The body height:length residuals were also the highest at 25°C (i.e. larvae had deeper or stockier bodies). The yolk sac was present up to 72 hph at 23 and 25°C, while it was entirely consumed after 48 hph in larvae held at 28 and 31°C. Larvae showed the fastest growth during the first 24 hph in all temperature treatments; this period corresponded to the highest energy consumption as determined by the decrease in yolk sac and oil‐globule volume. Eye diameter did not vary significantly with time during yolk‐resorption. We conclude that a temperature near 25°C is optimal for raising snook larvae during the yolk‐resorption period.     

The effect of temperature and dietary fat level on tissue lipid composition in Atlantic salmon (Salmo salar) fed wax ester‐rich oil from Calanus finmarchicus

Copepod oil (CO) from the marine zooplankton, Calanus finmarchicus, is a potential alternative to fish oils (FOs) for inclusion in aquafeeds. The oil is composed mainly of wax esters (WE) containing high levels of saturated fatty acids (SFAs) and monounsaturated fatty alcohols that are poorly digested by fish at low temperatures. Consequently, tissue lipid compositions may be adversely affected in salmon‐fed CO at low temperatures. This study examined the lipid and FA compositions of muscle and liver of Atlantic salmon reared at two temperatures (3 and 12 °C) and fed diets containing either FO or CO, supplying 50% of dietary lipid as WE, at two fat levels (～330 g kg^?1, high; ～180 g kg^?1, low). Fish were acclimatized to rearing temperature for 1 month and then fed one of four diets: high‐fat fish oil (HFFO), high‐fat Calanus oil (HFCO), low‐fat fish oil (LFFO) and low‐fat Calanus oil (LFCO). The fish were grown to produce an approximate doubling of initial weight at harvest (220 days at 3 °C and 67 days at 12 °C), and lipid content, lipid class composition and FA composition of liver and muscle were determined. The differences in tissue lipid composition between dietary groups were relatively small. The majority of FA in triacylglycerols (TAG) in both tissues were monounsaturated, and their levels were generally higher at 3 °C than 12 °C. Polyunsaturated fatty acids (PUFA), particularly (n‐3) PUFA, predominated in the polar lipids, and their level was not significantly affected by temperature. The PUFA content of TAG was highest (～26%) in the muscle of fish fed the HFCO diet at both temperatures. Tissue levels of SFAs were lower in fish‐fed diets containing HFCO than those fed HFFO, LFFO or LFCO, particularly at 3 °C. The results are consistent with Atlantic salmon being able to incorporate both the FA and fatty alcohol components of WE into tissue lipids but, overall, the effects of environmental temperature on tissue lipids were more pronounced in fish fed the CO diets than FO diets.     

Effect of rearing temperatures on the growth and maturation of Arctic charr (Salvelinus alpinus) during juvenile and on‐growing periods

The effect of rearing temperature on the growth and maturation of Arctic charr (Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October–April, size range 20–500 g) at constant temperatures of 9, 12 and 15 °C and according to two temperature‐step groups (T_step) i.e. fish transferred from 15 to 12 °C or from 12 to 9 °C. All the previous treatments were then reared either at 7 °C or at 12 °C for an additional 4 months (phase II, size range 300–1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 °C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 °C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 °C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase i.e. 4.18% (±0.79) and 7.29% (±0.89), for the temperature groups of 12 and 15 °C, respectively, compared with 2.49% (±0.74) for the 9 °C group. Our results suggest that for the production of fish >1000 g, moderate or low temperatures (here 9 °C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on‐growing period.     

Patterns of growth and nutrient deposition in lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis) and their hybrid, F1 splake (Salvelinus namaycush × Salvelinus fontinalis) as a function of water temperature

Several fish species of the genus Salvelinus are used for stocking freshwaters in North and South America and much of Europe but there is little information about their growth and carcass composition. Lake trout (S. namaycush), brook trout (S. fontinalis) and their hybrid F₁ splake (S. namaycush × S. fontinalis) (initial body weight ca. 2–4 g) were raised at 6.4, 10.6 and 14.9 °C to examine growth and nutrient deposition as a function of water temperature. In all species, weight gain and feed intake increased significantly with water temperature and feed efficiency was significantly lower at 6.4 than at 10.6 and 14.9 °C. In brook trout, Thermal‐unit Growth Coefficient (TGC) growth rate was significantly lower at 6.4 than at 10.6 and 14.9 °C, while in F₁ splake TGC was only lower at 6.4 than 10.6 °C. Expressed in terms of relative composition a significant effect of temperature was observed. In all species, moisture content decreased while crude protein, lipid, ash and energy contents increased with increased temperature. Expressed in absolute terms, however, a significant effect of temperature was not observed. In all species carcass contents increased significantly with increased live body weight and were best described by simple linear equations. Gross energy concentration was significantly affected by both water temperature and body weight. These data indicate that the growth of these species is a function of water temperature and, in absolute terms, carcass composition is mainly a function of body weight and not water temperature. Also, such simple linear equations bode well for modification of existing feed requirement and waste outputs models; improving their applicability to these species.     

The effect of water temperature on growth parameters of intensively reared juvenile peled Coregonus peled

The effect of water temperature on growth and food intake of juvenile peled Coregonus peled was tested with specimens of initial age 75 days and 230 days posthatching (dph). The 75‐day group (initial body weight 0.6 ± 0.04 g) were reared for 63 days and 230‐day group (initial body weight 13.75 ± 2.93 g) for 42 days at temperatures of 13, 16, 19, 22 and 25°C under 12:12 L:D photoperiod. The optimal temperature range for the 75 dph fish was found to be 19–22°C. The fish reached final mean weight of 9.7 ± 2.5 g at 19°C and 9.0 ± 2.7 g at 22°C. Final mean weight of 230 dph fish did not differ significantly among temperature groups. Mortality increased at higher temperatures, with the critical temperature of 25°C for both age groups. Maximum food intake (19.0 ± 4.7, 18.8 ± 5.2, 18.6 ± 4.6 g kg^?1biomass) was observed in groups reared at temperatures of 19, 22 and 25°C with no significant differences among groups.     

Growth of juvenile common snook (Centropomus undecimalis Bloch, 1792) reared at different temperatures and salinities: Morphometric parameters,RNA/DNA,and protein/DNA ratios

We investigated the growth of juvenile common snook (Centropomus undecimalis) reared at 25°C and 28°C and salinities of 0.3, 15, and 32 g L^?1. Total length, weight, RNA/DNA, and protein/DNA ratios were determined after 90 days of experiment. Higher growth was observed at 28ºC compared with 25°C, at the same salinity. At 28°C and 15 g L^?1 salinity, the weight (25.14 g) of juveniles was twice that of the juveniles reared at the lower temperature. At different salinities, only higher temperature affected growth, with higher weight values obtained at 15 g L^?1 in comparison with 0.3 and 32 g L^?1. Length was similar at 0.3 and 15 g L^?1. The RNA/DNA ratio was greater in juveniles reared at a salinity of 15 g L^?1 when compared with 0.3 and 32 g L^?1. This study shows that the combination of higher temperature and intermediate salinity promotes better growth of common snook juveniles.     

Performance of Albino and Normal Channel Catfish (Ictalurus punctatus) in Different Water Temperatures

Experiments to determine effects of skin colour on growth in different water temperatures were conducted with albino and normally pigmented channel catfish (Ictalurus punctatus). In Experiment 1, fish were reared in 29°C, 27°C, or 22°C water from hatching to 40 weeks of age. Two additional groups were initially reared in 27°C water for either 12 or 16 weeks and in 22°C water for either the remaining 28 or 24 weeks, respectively. Results indicated that: (1) albino fish reared in 29°C water were superior in growth to normal fish; (2) albino fish did not differ from normal fish in growth when reared in either 27°C or 22°C water; (3) albino fish were inferior in growth to normal fish when reared in 27°C water for either 12 or 16 weeks of the 40-week growth period; (4) genetic differences between families and the age of fish strongly influenced relative growth of both colour types; and (5) both albino and normal catfish were able to compensate in growth at a later age. Experiment 2 began when fish were 48 weeks old and included both albino and normal fish which were either full-siblings or not genetically related. Results indicated that: (1) albinos and normal catfish did not respond differently to a 5°C water temperature change; (2) genetically related and randomly selected albino and normal fish produced consistent results concerning water temperature, skin pigmentation, and sex effects on growth; (3) increasing water temperature from 22°C to 27°C for 19 weeks resulted in increased weight and length of the fish by 144 and 80%, respectively; and (4) growth increase during the first 19-week period resulting from the higher water temperature was followed by a significant increase in the subsequent 10-week growth when the fish were in the lower water temperature.