Size‐related oxygen consumption and ammonia excretion of Eurasian perch (Perca fluviatilis L.) reared in a recirculating system

Oxygen consumption (OC) and ammonia excretion rates (AE) of perch were measured under commercial‐like conditions (temperature 23.3 °C) in both fed (F) and feed‐deprived groups (D). Measurements were taken in triplicate in six sized batches of perch ranging from 44.8 to 336.2 g. The mean daily OC was 288.3–180.6 mg O₂ kg^?1 h^?1 for group F fish ranging in size from 44.8 to 279.4 g body weight. The mean daily AE expressed as total ammonia nitrogen (TAN) was 13.8–5.2 mg TAN kg^?1 h^?1 in the same groups. Daily peaks of OC in group F perch were observed 6 h after the onset of feeding for each size group with relatively stable values up to the end of feeding. Peaks of daily AE in group F perch were observed 10 h after the onset of feeding in each size group, with a rapid decrease up to 16 h after onset. In group D, OC was 181.1–110.5 mg O₂ kg^?1 h^?1 in the weight range 57.9–336.2 g. The daily mean AE was 1.7–0.5 TAN kg^?1 h^?1 in this group. No dramatic peaks of OC and AE were observed in group D perch.     

Rates of oxygen consumption and ammonia excretion of juvenile Eurasian perch Perca fluviatilis L.

The impact of feeding, fish size (body weight from 18.5 to 56.5 g) and water temperature (20 and 23 °C) on oxygen consumption (OC, mg O₂ kg^–1 h^–1) and ammonia excretion (AE, mg TAN kg^–1 h^–1) was studied in Eurasian perch held in recirculation systems. OC for both fed and feed-deprived (3 days) fish was higher at 23 °C (278.5 and 150.1 mg O₂ kg^–1 h^–1) than at 20 °C (249.3 and 135.0 mg O₂ kg^–1 h^–1; P < 0.01). AEs for both fed and feed-deprived fish were also significantly higher at 23 °C than at 20 °C (P < 0.001). Water temperature and fish size had a significant impact on the oxygen:feed ratio (OFR, kg O₂ kg^–1 feed fed day^–1) and ammonia:feed ratio (AFR, kg TAN kg^–1 feed fed day^–1; P < 0.001). Their average values at temperatures of 20 and 23 °C were 0.17 and 0.19 kg O₂ kg^–1 feed fed day^–1 and 0.009 and 0.011 kg TAN kg^–1 feed fed day^–1, respectively.     

Effects of feeding frequency on metabolism of juvenile walleye

The effects of feeding frequency (1, 2, 3, or 15 times daily) on oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion, (AE, mg TAN kg⁻¹ h⁻¹) of walleye (Stizostedion vitreum) are described. Walleye were reared at a practical culture density of 35·4 kg m⁻³ in a single-pass system at 23·2°C. Diurnal variation in metabolic rates were related to feeding, not to photoperiod. Minimum OC rates occurred 30 min before the first feeding of the day, which was the longest average time since the last feeding. Metabolic rates increased immediately after feeding. The maximum rates for OC were 36–49% higher than the minimum rates, and 14–22% higher than the 24-h mean rate. Maximum rates for AE were 137–409% higher than the minimum rates, and 39–87% higher than the mean rates. There was a highly significant difference in the mean metabolic rates related to feeding frequency. The mean OC rate for 1 feeding day⁻¹ (222·0 mg O₂ kg⁻¹ h⁻¹) was greater than the mean rates for 2, 3 and 15 feedings day⁻¹. The OC rate for 1 feeding day⁻¹ was 50·6% greater than the rate for 15 feedings day⁻¹ (147·4 mg O₂ kg⁻¹ h⁻¹), the lowest mean rate. Mean and maximum oxygen/feed ratio (OFR, kg O₂ kg⁻¹ feed fed day⁻¹), varied inversely with feeding frequency. The mean ammonia/feed ratio (AFR) was similar for all but the 3 feedings day⁻¹ treatment, but the maximum AFRs for 2 and 15 feedings day⁻¹ were lower than the AFRs for 1 and 3 feedings day⁻¹. AE was directly proportional to OC; the regression equations were highly significant, but specific for feeding frequency.     

Tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.) larvae rearing under controlled conditions: density and basic supply of <Emphasis Type="Italic">Artemia</Emphasis> nauplii as the sole food

After artificial reproduction of tench, larvae must be maintained indoors, and studies on rearing conditions are needed, focussing on the reduction of labour and costs. Three experiments on larvae (5th day post-hatch) were conducted for 25 days using Artemia nauplii as the sole food in order to determine basic feeding and density conditions during the first rearing period. Tench were maintained in 25 l fibreglass tanks, supplied with an artesian water flow throughout of 0.2 l min⁻¹. Water temperature was 22.5 ± 1°C, and the photoperiod was natural. Larvae fed on a restricted amount of nauplii reached high survival rates, even with the minimum of 50 nauplii larva⁻¹ day⁻¹. This amount of food may be sufficient at least for the first 25 days of exogenous feeding if fast growth is not the priority, and high densities can be maintained with good survival rates (over 90% up to 160 larvae l⁻¹ and 77% with 320 larvae l⁻¹). When food was supplied in excess once a day, high survival rates were achieved (91–97%), without differences among the densities tested. Animals at a density of 100 l⁻¹ reached the highest length (15.57 mm) and individual weight (46.8 mg). This growth is greater than those reported in studies feeding several times a day. It could be deduced that, while live food remains available for tench, it is not necessary to feed so frequently. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.     

Nitrogen and phosphorus digestibility and excretion of different-sized groups of milkfish (Chanos chanos Forsskal) fed formulated and natural food-based diets

This study determined the digestibility of nitrogen and phosphorus, and the excretion rate of different‐sized groups of milkfish fed a commercial diet, a SEAFDEC formulated diet or lab‐lab (natural food‐based diet). Fish (31.2–263.0 g) were stocked in 12 units of 300‐L fibreglass tanks filled with aerated seawater. The postprandial total ammonia‐nitrogen (TAN) and phosphate (PO₄‐P) excretion of fish were estimated from changes in TAN and PO₄‐P concentrations in water for 24 h. Digestibility was determined from the nitrogen, phosphorus and Cr₂O₃ content of the diets, and pooled faeces after the fish had been fed diets marked with chromic oxide. TAN excretion rate (mg TAN kg^?1 fish day^?1) was significantly lowest (P < 0.05) in medium to very big fish fed the lab‐lab diet (60.8–124.4) and highest in small and medium fish fed the SEAFDEC diet (333.3–331.6) and small fish fed the commercial diet (280.1). Regardless of size, fish fed lab‐lab excreted (mg PO₄‐P kg^?1 fish day^?1) significantly lower PO₄‐P (36.2) but did not differ with fish fed the commercial diet (64.8). Excretion rates decreased exponentially as fish weight increased but positively increased with feed ration. Excretion pattern of milkfish revealed two peaks: the first peak occurred 6 h after feeding and the second peak at 18 h for TAN and 21 h for PO₄‐P, coinciding with the start of the daylight hours. TAN and PO₄‐P excretion accounted for 20.5–34.6% of total N consumed and 18.7–42.6% of P consumed respectively. Approximately 27.9–42.5% of N consumed and 47.2–58.5% of P consumed were lost as faeces. Total nutrient losses were lower using the lab‐lab diet (0.31 g N and 0.14 g P kg^?1 fish) compared with the formulated diets (0.47–0.48 g N and 0.17–0.19 g P kg^?1 fish); the losses decreased per kg of fish as fish size increased. Results suggest that the diet and size of fish influence wastage of N and P to the environment with greater losses in small fish and when artificial diets are used. Such measurements will provide valuable information for the preparation of N and P budgets for milkfish in grow‐out systems.     

Oxygen consumption and ammonia excretion of common wolffish Anarhichas lupus Linnaeus 1758 in an experimental-scale, seawater, land-based culture system

The oxygen consumption (0₂) and ammonia excretion (N) of juvenile and adult common wolffish was measured in culture tanks in the laboratory. The oxygen consumption and ammonia excretion were affected by temperature (C), fish size and feeding rate. For juveniles (0.5 kg; 7C) the diel oxygen consumption rate varied between 37 and 62 mg O₂ kg^-1 h^-1 and ammonia excretion between 2.3 and 5.7 mg N kg^-1 h^-1. The corresponding rates for adult fish (6.9 kg; 7C) were 29-44 mg O₂ kg^-1 h^-1 and 1.2–3.1 mg N kg^-1 h^-1. The weight-specific oxygen consumption (mg O₂ kg^-1 h^-1) was described by the following formulae: O₂ (7C) = 0.17* W^0.83 and O₂ (12C) = 0.39 * W^0.73 and the corresponding ammonia excretion (mg N kg^-1 h^-1) by: N(7C) = 0.024 W^0.75 and N(12C) = 0.073 W^0.60, where W is fish weight in g.     

Studies on digestibility and digestive enzyme activities in Labeo rohita (Hamilton) juveniles: effect of microbial α-amylase supplementation in non-gelatinized or gelatinized corn-based diet at two protein levels

A 60-days feeding trial was conducted to delineate the effect of both gelatinized and non-gelatinized corn with or without supplementation with exogenous α-amylase at two dietary protein levels (35% and 28%) on dry matter digestibility, digestive enzymes and tissue glycogen content of Labeo rohita juveniles. Three hundred and sixty juveniles (average weight 10±0.15 g] were randomly distributed into 12 treatment groups with each of two replicates. Twelve semi-purified diets containing either 35% or 28% crude protein were prepared by including gelatinized (G) or non-gelatinized (NG) corn as carbohydrate source with different level of microbial α-amylase (0, 50, 100 and 150 mg kg⁻¹). The dry matter digestibility of G corn fed groups was significantly higher (P < 0.05) than that of the NG corn fed groups. Hepatosomatic index (HSI), liver glycogen and intestinal amylase activity of G starch fed groups were significantly higher (P < 0.05) than those of the NG corn fed groups. However, the reverse trend was found for gastrosomatic index (GSI), muscle glycogen and intestinal protease activity. Addition of 50 mg α-amylase kg⁻¹ feed improved the dry matter digestibility of NG starch fed groups, which was similar to that of the G corn fed groups or NG corn supplemented with 100/150 mg α-amylase kg⁻¹ feed. HSI, liver glycogen and intestinal amylase activity were significantly increased (P < 0.05) at minimum level of α-amylase in the feed (50 mg kg⁻¹) and did not increase due to further inclusion of amylase in the diet. Supplementation with α-amylase at 50 mg kg⁻¹ increased the intestinal amylase activity beyond which no significant changes were observed. Protease activity of liver and intestine was highest (P < 0.05) in higher crude protein (CP) fed groups, but protease activity of the intestine was significantly higher in the α-amylase supplemented groups. Hence, it was concluded that feed with 28% CP containing either G corn without α-amylase or NG corn with 50 mg α-amylase kg⁻¹ may be used as the alternative carbohydrate source for L. rohita juveniles.     

The effect of synthetic and natural pigments on the colour of the cichlids (<Emphasis Type="Italic">Cichlasoma severum</Emphasis> sp., Heckel 1840)

In this study, we have investigated the effects of Porphyridium cruentum (Rodophyta) as a natural pigment source and astaxanthin and β-carotene as synthetic pigment sources on the skin colour of cichlid fish (Cichlasoma severum sp., Heckel 1840), which are generally light orange with white patches and becomes shiny orange in the reproductive phase. The fish were fed diets containing 50 mg kg⁻¹ astaxanthin and β-carotene, and P. cruentum powder. The amount of both natural and synthetic pigment sources given as feed was 50 mg kg⁻¹, and the experiment was continued for 50 days. Total carotenoid content of the fish was determined spectrophotometrically at the end of the experiment. As a result, while a visible change of colour in the skin of the fish fed on the feed containing astaxanthin was observed with 0.34 ± 0.2 mg g⁻¹ of pigment accumulation, a relatively small change of colour was observed in the skin of other fish that were fed on the feed containing P. cruentum and β-carotene with 0.22 ± 0.2 mg g⁻¹ and 0.26 ± 0.1 mg g⁻¹ of pigment accumulations, respectively. Therefore, it was determined that these pigment sources have an effect on the colour of cichlid fish.     

Ammonia excretion rates from post-smolt Atlantic salmon, Salmo salar L., in land-based farms

Empirical data on ammonia excretion rates were compiled from several published and unpublished growth studies on post-smolt Atlantic salmon, Salmo salar L. Fish in all studies were fed to satiation with commercially produced high-energy diets (ME = 18–19 MJ kg^-1) with a protein content of 40–45%. About 35 ± 3% (mean SE) of the nitrogen supplied to fish was excreted as total ammonia (TAN = NH₃-N + NH₄⁺-N). The results of a linear regression analysis of N intake to N excretion demonstrated, however, that TAN excretion rates could be divided into two components: TAN_excretion [g N kg fish^-1 day^-1] = 0.036 + 0.26 N_intake [g N kg fish^-1 day^-1]. The intercept of the regression equation indicates that the endogenous TAN excretion rates in post-smolts could be estimated as 36 mg TAN kg fish^-1 day^-1, and about 26% of the nitrogen supplied to the fish was excreted postprandially. This postprandial TAN excretion was lower than that from other salmonid species fed low-energy diets. The daily maximum TAN excretion rate was about 43% higher than daily mean values, which agree with several studies. The ammonia quotient (A.Q.) measured was independent of the nitrogen supplied, and was calculated as 0.112. The outputs from the present model were compared to those from other ammonia excretion models.     

Effects of cyclic and regular feeding of a Quillaja saponin supplemented diet on growth and metabolism of common carp (Cyprinus carpio L.)

Fifteen common carp weighing 19.2±2.9 g were reared individually in chambers of a respirometer system which allowed feeding, and continuous measurement of oxygen consumption. The fish were divided into three groups of 5 each, and were given control feed (C group), control feed supplemented with 150 mg kg⁻¹ of Quillaja saponins (QS) (S150 group), and control and the saponin supplemented diet during alternate weeks (S150b group), for 56 days. Supplementation with QS at a level of 150 mg kg⁻¹ caused a significant (P<0.05) increase in metabolic growth rate, food conversion efficiency (FCE), protein productive value (PPV) and apparent lipid conversion (ALC) of carp, even as the metabolic rate was lower than the C group. The efficiency of energy utilisation indicated by parameters such as energy expenditure (EE), energy retention (ER) and amount of oxygen consumed per unit body mass gain (OPM) were also significantly (P<0.05) better in the S150 group. The performance of the S150b group was intermediate between the C and S150 group in this experiment. Possible reasons for the effects of dietary QS are discussed. It was concluded that there has to be continuous dietary supply of QS at the level of 150 mg kg⁻¹, for maximum positive effects of these substances on growth of common carp. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in commercially exploited populations of tench, Tinca tinca (L.), in littoral zones of lakes of northeastern Poland

Commercially exploited tench, Tinca tinca, (L.) populations in 480 lakes in the northeastern Poland were analyzed on the basis of the fishery data from 1949 to 1994. The long-term changes in tench catch were studied in four categories of lakes with respective proportions of littoral zones (<30, 31–60, 61–90 and <90% of total lake area). The analyses were performed with using relative catch (kg ha⁻¹ month⁻¹) of tench. Mean relative catch of tench for 1949–1994 ranged from 0.36 kg ha⁻¹ month⁻¹ in lakes with smallest littoral zone (>30%) to 0.93 kg ha⁻¹ month⁻¹ in lakes with the largest littoral (<90%). Mean relative catch increased with increasing proportions of littoral zones in lakes. However, long-term trends in mean relative catch of tench showed decreasing tendencies in all lakes. The beginning of these tendencies was found about ten years earlier in lakes with smaller littoral (<60%) in comparison to lakes with larger littoral zones (>60%). Mean stocking rates of tench (number of 1-year-old fish per ha of littoral) for 1949–1994 were not significantly different in lakes of studied categories. However, lakes with proportionally less littoral zone had reduced stocking efficiency estimated as number of stocked fish per ha of littoral to require 1 kg ha⁻¹ month⁻¹ of tench.     

Optimum ration level for better growth,conversion efficiencies and body composition of fingerling <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

The effects of ration levels on growth, conversion efficiencies and body composition of fingerling Heteropneustes fossilis (6.8 ± 0.04 cm, 5.0 ± 0.02 g) were studied by feeding isonitrogenous (40% crude protein) and isocaloric (19.06 MJ kg⁻¹ gross energy) diets representing 1, 3, 5, 7 and 9% of the body weight (BW) day⁻¹ to triplicate groups of fish . Growth performance of the fish fed at the various ration levels was evaluated on the basis of live weight gain percentage (LWG%), feed conversion ratio (FCR), specific growth rate percentage (SGR%), protein retention efficiency (PRE%) and energy retention efficiency (ERE%) data. Maximum LWG% and SGR were obtained at a feeding rate of 7% BW day⁻¹, whereas best FCR (1.6), PRE% and ERE% were recorded at a feeding rate of 5% BW day⁻¹. Maximum body protein was also obtained for the group receiving the diet representing 5% of their body weight. However, a linear increase in fat content was noted with the increase in ration levels up to 7% BW day⁻¹. The SGR, FCR, PRE and ERE data were also analyzed using second-degree polynomial regression analysis to obtain more precise information on ration level, with the results showing that the optimal ration for these parameters was 6.8, 6.1, 5.9 and 6.2% BW day⁻¹, respectively. Based on the above second-degree polynomial regression analysis, the optimum ration level for better growth, conversion efficiencies and body composition of fingerling H. fossilis was found to be in the range of 5.9–6.8% of the BW day⁻¹, corresponding to 2.36–2.72 g protein and 88.20–101.66 MJ digestible energy kg⁻¹ diet day⁻¹.     

Gastrointestinal and metabolic effects of feeding schedule on voluntary feed intake and growth of European eel, <Emphasis Type="Italic">Anguilla anguilla</Emphasis>

Gastrointestinal and metabolic influences on short- and medium-term control of voluntary feed intake of European eel were investigated for groups of fish fed at different feeding schedules: 1 meal 2 days⁻¹, 1 meal day⁻¹, 2 meals day⁻¹ and continuous feeding for 12 h and 24 h daily. For fish fed daily, the feeding schedule had no effect on feed intake, metabolism, growth, size variation and body composition. Only fish fed once every 2 days could not completely compensate by increasing their average meal size and showed a reduced feed intake, metabolism and growth. Stomach capacity did not limit meal size and feed intake as large differences in appetite were found for eels with empty stomachs. Feed intake was related to metabolism as the levels of O₂ consumption and NH₄ excretion just before the meal were correlated to average meal size, suggesting that rate (and duration) of metabolism is sensed and is providing information about the metabolic consequences of feed intake and feed processing. Meal size is based on the (expected) scope for metabolism and eels seem to strive to an average daily feed intake, associated with their developmental state (growth potential). Plasticity in this feed intake behaviour, expressed by individual variation in feed intake and day-to-day fluctuations in individual and group intake, is regarded as adaptive on different time scales.     

Influence of diet and feeding strategy on the performance of nitrifying trickling filter,oxygen consumption and ammonia excretion of gilthead sea bream (Sparus aurata) raised in recirculating aquaculture systems

Gilthead sea bream (Sparus aurata) was raised in six individual recirculating aquaculture systems (RAS) whose biofilters’ performance was analyzed. Fish were fed with three different diets (a control diet, a fishmeal-based diet (FM), and a plant meal-based diet (VM)) and with three different feeding strategies (manual feeding to apparent satiation, automatic feeding with restricted ration, and auto-demand feeding). For every combination of diet and feeding strategy, the mean oxygen consumption, ammonia excretion, and ammonia removal rate were determined. Fish fed with the VM diet consumed the most oxygen (20.06?±?1.80 gO₂ consumed kg^?1 day^?1). There were significant differences in ammonia excretion depending on the protein content and protein efficiency of the diet, as well as depending on feeding strategy, which in turn affected ammonia removal rates. Fish fed by auto-demand feeders led to the highest mean ammonia removal rate (0.10 gN-TAN removed m^?2 biofiltration area day^?1), while not leading to peaks of high ammonia concentration in water, which preserve fish welfare and growth.

     

Feces Production and Ammonia Excretion of Pacific Abalone,Haliotis discus hannai,Fed Kelp,Laminaria japonica,in Relation to Water Temperature and Shell Length

Nitrogen excreted by aquatic animals mainly takes the form of metabolic wastes such as feces and ammonia, which is accumulated in the intensive aquaculture system and causes serious environmental contamination. So it is very important to determine the waste excretion characteristics of aquatic animals for the development of practical and nonpolluting land‐based aquaculture. Abalone has a unique feeding habit and feeding regime, different from those of finfish; abalone gnaw feed seaweed to produce feces and ammonia continuously. In this study, the rates of feces production and ammonia excretion of pacific abalone, Haliotis discus hannai, of three shell lengths (3, 5, and 7 cm) were investigated under three different temperature conditions (12, 16, and 20 C). All experiments were performed in triplicate in a semirecirculating aquaculture system. Feces were collected for 5 d, and ammonia concentrations (total ammonia nitrogen [TAN]) in the tank inlet and outlet were monitored every 4‐h interval for 24 h at the fourth day of the feces collection. The regressions for the weight‐specific feces production rate (g feces/kg abalone/d) and the weight‐specific TAN excretion rate (mg TAN/kg abalone/d) in relation to water temperature (T, C) and shell length (L, cm) were weight‐specific feces production rate = exp(1.575 ? 281.2/T² – 0.142L), r² = 0.9550, and weight‐specific TAN excretion rate = exp(5.052 ? 277.1/T² ? 0.136L), r² = 0.9598. Pacific abalone produced 108.3–111.7 g feces and excreted 3.83 g TAN/kg seaweed ingested (dry weight).     

Standard oxygen consumption of seasonally acclimatized cownose rays, Rhinoptera bonasus (Mitchill 1815), in the northern Gulf of Mexico

Standard oxygen consumption rate (MO₂) was determined for 19 cownose rays (Rhinoptera bonasus) using flow-through respirometry. Rays ranged in size from 0.4 to 8.25 kg (350–790 mm DW). Respirometry experiments were conducted on seasonally acclimatized rays at temperatures from 19.0 to 28.8 °C. Estimates of mass-dependent MO₂ ranged from 55.88 mg O₂ kg⁻¹ h⁻¹ for an 8.25 kg ray to 332.75 mg O₂ kg⁻¹ h⁻¹ for a 2.2 kg animal at 22–25°C. Multiple regression analysis examining the effect of temperature, salinity, and mass on standard mass-independent MO₂ found temperature (P < 0.01), and mass (P < 0.0001) to have a significant effect on oxygen consumption, whereas salinity did not (P > 0.05). Q ₁₀ was calculated as 2.33 (19–28 °C), falling between the estimates determined for two other batoid species, the bull ray (Myliobatos aquila; Q ₁₀ = 1.87) and the bat ray (Myliobatis californica; Q ₁₀ = 3.00). The difference in the Q ₁₀ estimates may be attributed to the use of seasonally acclimatized as opposed to laboratory-acclimated animals.     

Effect of oral administration of l -thyroxine (T4) on growth performance, digestibility, and nutrient retention in Channa punctatus (Bloch) and Heteropneustes fossilis (Bloch)

Effects of oral administration of l-thyroxine (T₄) on growth performance, body composition, and some aspects of nutritional physiology were investigated in two slow-growing air-breathing fish (Channa punctatus and Heteropneustes fossilis) under laboratory conditions (LD 12:12 at 25°C). The results indicate that irrespective of the species, fish fed diets containing lower doses of T₄ (up to 50 mg kg⁻¹ of diet in C. punctatus and up to 100 mg kg⁻¹ of diet in H. fossilis) showed significantly (P < 0.05) higher growth (in terms of live weight and length gain, specific growth rate, percentage gain in body weight and condition factor), low feed conversion ratio, high nutrient retention, high apparent protein digestibility, and high digestive enzyme activity. Viscero-somatic (VSI) and hepato-somatic (HSI) values were also high in fish fed on low dietary T₄ levels. Liver glycogen levels decreased with the increase in the dietary T₄ levels, indicating its utilization during growth. Muscle glycogen levels in H. fossilis coincided with high growth at 100 mg of T₄. Observation of the postprandial excretion of metabolites (N–NH₄ ⁺ and o-PO₄ ⁻) indicated significantly (P < 0.05) low levels in aquaria water where the fish were fed diets with low T₄ levels. These studies further revealed that feeding fishes on higher T₄ levels (above 50 mg in C. punctatus and above 100 mg in H. fossilis) not only repressed growth performance and nutrient retention, but also affected carcass composition by lowering protein accumulation (muscle and carcass protein) and energy assimilation. These studies revealed a biphasic action of thyroxine, i.e., the hormone at lower doses is anabolic, while at higher doses it acts as a catabolic agent, indicating that feeding fishes on higher doses can be detrimental to their growth and metabolism. In summary, the results of the present study show that feeding H. fossilis and C. punctatus on low doses of T₄ enhances growth, decreases excretion of metabolites, and increases nitrogen retention. These observations suggest that T₄ supplementation of the diet may have practical utility in the culture of slow-growing fish species.     

A dynamic fish digestion–assimilation model: oxygen consumption and ammonia excretion in response to feeding

Soon after feeding, fish metabolism increases, resulting in high rates of oxygen consumption (OC) and ammonia excretion (AE). In intensive aquaculture, these peaks must be treated as they occur, requiring water-conditioning equipment of high installed capacity. Shaving off the peaks by more frequent feeding reduces the required capacity, but to do that properly, a dynamic prediction model of fish OC and AE is required. Recent experimental OC and AE data from the literature are used to fit a simple, four-compartment (four-state variable) mechanistic digestion–assimilation model to three feeding-frequency treatments. As the AE data are well correlated with the OC data, the dynamic model is used first to predict OC, and then the correlation is used to calculate the corresponding AE. The OC model is composed of a five-parameter, static submodel and a dynamic part with five additional parameters. The latter are fitted with the time-varying data. The resulting fit, to all treatments with the same set of parameters, is good. The dynamic model mimics properly the plateau evident in the once-per-day feeding treatment, as well as the curvatures of the ascending and descending segments. The static portion of the model, based mostly on daily totals, predicts a linear dependence of daily OC and AE on the size of the daily feed ration, in agreement with the data. Notation: Time unit in this list is day (d). Some of the rates in the text are presented per hour, for convenience. Components of the energy balance are presented here in kJ. In the text, they are evaluated in terms of oxygen equivalents. Temperature is specified here in K, but the empirical equations in the text require °C.     

Evaluation of three types of structured floating plastic media in moving bed biofilters for total ammonia nitrogen removal in a low salinity hatchery recirculating aquaculture system

Three different commercially available structural plastic media were evaluated in triplicate in moving bed biofilters under low salinity (11–12 ppt) warm water culture conditions and two different feed loading rates. The culture system consisted of nine separate modules that include a double drain fish culture tank paired to a moving bed biofilter. The biofilters were filled with 0.11 m³ of one of three different types of floating plastic structured media. The three types of media evaluated were K1 kaldnes media, MB3 media, and AMB media. Volumetric total ammonia nitrogen (TAN) removal rates (g TAN removed/m³ media-day), TAN removal efficiency, and biofilm kinetic constants, K_i (h⁻¹) were determined for the three media types at two different daily feed load rates of 3.5 and 8.2 kg feed/m³ media. The feed provided was a 4.8 mm slow sinking marine grower diet pellet (45% protein, 17% fat). Average (±standard deviation, SD) volumetric TAN removal rates (VTR) at the lower feed load for the three media types were 92.2 ± 26.3, 86.1 ± 27.5, and 82.5 ± 25.9 for the MB3, AMB, and K1 kaldnes media, respectively. At the higher feed load the average VTR for the three media types was 186.4 ± 53.7, 172.9 ± 47.8, and 139.9 ± 38.9 for the MB3, AMB, and K1 kaldnes media, respectively. Influent TAN concentrations varied by the feed load rate and ranged from 0.55 to 0.93 mg/L and 0.83 to 1.87 mg/L for the low and higher feed loads, respectively. The percent TAN removal rates for the MB3 media was the highest of the three media types at both the low and high feed load rates averaging 12.3% and 14.4%, respectively. The MB3 media was selected for use in the moving bed biofilters because of the greater VTR and removal efficiency results for use in the 0.11 m³ moving bed biofilters of the hatchery recirculating aquaculture system.     

Nitrogenous and phosphorus excretions in juvenile silver catfish (Rhamdia quelen) exposed to different water hardness, humic acid, and pH levels

This study examined ammonia, urea, creatinine, protein, nitrite, nitrate, and phosphorus (P) excretion at different water hardness, humic acid, or pH levels in silver catfish (Rhamdia quelen) juveniles. The fish were exposed to different levels of water hardness (4, 24, 50, or 100 mg L^?1 CaCO₃), humic acid (0, 2.5, or 5.0 mg L^?1), or pH (5.0, 6.0, 7.0, 8.0, or 9.0) for 10 days. The overall measured nitrogen excretions were 88.1 % (244–423 μmol kg^?1 h^?1) for ammonia, 10.9 % (30–52 μmol kg^?1 h^?1) for creatinine, 0.02 % (0.05–0.08 μmol kg^?1 h^?1) for protein, 0.001 % (0.002–0.004 μmol kg^?1 h^?1) for urea, 0.5 % (0.64–3.6 μmol kg^?1 h^?1) for nitrite, and 0.5 % (0.0–6.9 μmol kg^?1 h^?1) for nitrate, and these proportions were not affected by water hardness or humic acid levels. The overall P excretion in R. quelen was 0.14–2.97 μmol kg^?1 h^?1. Ammonia excretion in R. quelen usually was significantly higher in the first 12 h after feeding, and no clear effect of water hardness, humic acid levels, and pH on this daily pattern of ammonia excretion could be observed. Water hardness only affected the ammonia and P excretion of R. quelen juveniles in the initial and fifth days after transfer, respectively. The exposure of this species to humic acid increased ammonia excretion after 10 days of exposure but did not affect P excretion. An increase in pH decreased ammonia and increased creatinine excretion but did not change P excretion in R. quelen. Therefore, when there is any change on humic acid levels or pH in the culture of this species, nitrogenous compounds must be monitored because their excretion rates are variable. On the other hand, P excretion rates determined in the present study are applicable to a wide range of fish culture conditions.