Influence of fish size and water temperature on the metabolic demand for oxygen by barramundi, Lates calcarifer (Bloch), in freshwater

Oxygen demand by all animals is driven primarily by their needs for sustaining metabolism. Typically, larger animals require more oxygen and cellular fuel to carry out respiration than smaller animals. This relationship in most cases is not linear and is usually described by a coefficient and exponent (e.g. ax^b): the exponent b showing the relationship between live‐weight and energy/oxygen demand and is often termed the metabolic body weight (MBW) exponent, while the coefficient (a) tends to be temperature specific and describes the relationship between MBW and maintenance metabolic energy and oxygen demand at that specific temperature. Across all temperatures (range 26.0–32.0°C), the relationship between barramundi (Lates calcarifer) live‐weight (x; g) and relative oxygen consumption as standard metabolic rate (y; mg O₂ kg^?1 h^?1) at 29.4±1.5°C (mean±SD) was described by the exponential curve: y=710.19 x^?0.3268, R²=0.6875 (n=222 assessments). Examination of the same data but on a gross oxygen consumption (mg O₂ h^?1) basis showed a relationship between live‐weight (x; g) and gross oxygen consumption (y; mg O₂ h^?1) that was described by the exponential curve: y=0.710 x^0.6732, R²=0.9033. Evaluation of the combined relationship between fish live‐weight (y; g) and water temperature (x; °C) on gross oxygen consumption rate (z; mg O₂ h^?1) was described by the equation: z=(?20.7818+1.4017x?0.0227x²) ×y^0.673.     

Adapting bioenergetic factorial modelling to understand the implications of heat stress on barramundi (Lates calcarifer) growth,feed utilisation and optimal protein and energy requirements – potential strategies for dealing with climate change?

The implications of temperature on bioenergetics for barramundi (Lates calcarifer) were defined in an improved factorial model that encompassed revised parameters accounting for effects over the temperature range of 16–39 °C and size range of 10–3000 g. A revised growth function describing weight gain by barramundi as a function of fish weight and temperature was derived from farm and laboratory data and included a term for a shift in optimal temperature with fish size: Gain (g fish^?1 day^?1) = (K + xT + yT ² + zT³) * (weight)^ax+b. Maintenance energy and protein demand functions were also derived on a similar form, and all three functions combined to form the basis of a factorial model for energy and protein demand. Using this model, optimal iterative feed specifications were defined for a range of fish sizes at temperatures of 25, 30 and 35 °C. A feed demand model was also developed based on the demand for digestible energy (DE) at each of these temperatures. The model shows that at high temperatures (35 °C), there is an increase in digestible protein (DP) to DE demand, and that with increasing size, there is a decrease in the DP to DE demand.     

Indicators of genetic variation for feed conversion efficiency in black bream

Feed conversion efficiency (FCE) is a composite measure that combines feed intake with growth rate to estimate the effectiveness by which feed is converted to saleable meat product, and is a major determinant of production system efficiency. We measured the relationships between feed intake to apparent satiety and weight gain in replicate half‐sib families of black bream at four times over a 56‐day test period. After 42 days, we found significant additive genetic variance in both weight gain and feed intake, and a stabilization in family group variation in both traits. This indicates that 42 days is the minimum test period over which to measure genetic variation for FCE in black bream. There were high, positive phenotypic (and probably genetic) correlations between weight gain and feed intake after 42 days. We found no detectable genetic variation for either feed efficiency (weight gain/feed intake), or residual feed intake, which is a linear function that distinguishes between the amount of feed intake that is used for body maintenance and that used for growth. We argue that selection for improved FCE might be better achieved not by using a composite measure, but by using a weighted selection index that accounts for the genetic covariance among weight gain, feed intake and other key production traits.     

An assessment of cereal grains and other starch sources in diets for barramundi (Lates calcarifer) – implications for nutritional and functional qualities of extruded feeds

This study examined the digestibilities of whole diets and ingredients of a range of starch/cereal grains when fed to barramundi (Lates calcarifer). The ingredients included wheat, oats, sorghum, triticale, barley, among others. Twelve diets were prepared using a twin‐screw extruder to mimic modern aquafeed‐manufacturing processes. The diets were then fed to juvenile barramundi and the faeces collected using stripping methods. Significant variability in the digestible energy and starch value was seen among the test ingredients and diets. Diet starch digestibility ranged from 49.1% to 93.9%. Ingredient starch digestibility ranged from 18.0% to 96.5%. Among the different starch ingredients, a strong negative correlation between the ingredient amylopectin content and starch digestibility of that ingredient was observed. This relationship was also mirrored by a similar relationship, although not as strong, between total starch and starch digestibility. This study demonstrates that barramundi have limited ability to digest starch and that there is an effect of inclusion level on the ability of the animal to digest this nutrient. But it also demonstrates that there is a wide range of cereal sources that can be effectively used as starch sources in extruded diets for this species.     

Evaluating options for fishmeal replacement in diets for juvenile barramundi (Lates calcarifer)

Two experiments were conducted to examine critical thresholds to fishmeal inclusion in diets for barramundi and also the suitability of a range of different raw materials as alternative protein sources for this species. The first experiment used two diets formulated to the same digestible protein and energy specifications, which were then used to create a series of blended experimental diets that varied in fishmeal content from 0 to 770 g kg^?1. An additional diet containing sodium sulfamerazine was used as a negative control. Feed intake was unaffected with diets containing as little as 11% fishmeal, although broken‐line regression suggests that an inclusion of ～150 g kg^?1 fishmeal is a more likely threshold value. In a second experiment, a further series of diets was formulated for juvenile barramundi according to digestible protein and energy specifications predicted by existing bio‐energetic models. Each of the test raw materials was substituted for fishmeal at either 200 or 300 g kg^?1 (dependent on formulation or extrusion limitations), and two additional diets were included to examine two practical formulations. A diet with only fishmeal as the protein source was included as a reference. Each diet was produced using an APV19 twin‐screw extruder and then vacuum infused with the specified fish oil allocation. Each of the diet pellets produced was also characterized for a range of physical parameters. Fish of an initial weight of 70 ± 0.6 g fish^?1 were randomly allocated across 24 tanks with three replicates per treatment. After 6 weeks, average weight gain across all treatments was 73 ± 12.7 g fish^?1 and feed conversion across all treatments averaged 0.94 ± 0.08 g fish^?1. None of the diets using alternative raw materials had poorer growth or feed conversion than the fishmeal‐based reference diet. The inclusion of either the lupin kernel meals or canola meal significantly improved both weight gain and feed conversion compared to the reference diet. The results from this study demonstrate that there is clear potential to replace the fishmeal content of diets for barramundi without loss of fish performance, up to and including diets with as little as 150 g kg^?1 fishmeal inclusion.     

A determination of the quantitative requirements for docosahexaenoic acid for juvenile barramundi (Lates calcarifer)

A series of diets with varying docosahexaenoic acid (DHA; 22:6n‐3) inclusion levels (1 g kg^?1 3 g kg^?1, 6 g kg^?1, 10 g kg^?1, 15 g kg^?1 and 18 g kg^?1) were fed to juvenile barramundi (Lates calcarifer) for 6 weeks. Two additional diets examined the addition of arachidonic acid (ARA; 20:4n‐6) or eicosapentaenoic acid (EPA; 20:5n‐3) to the diets at 10 g kg^?1 when DHA was also included at 10 g kg^?1. Fish were fed the diets on a pair‐fed feeding regime to eliminate feed intake variability. Fish were weighed, and blood and tissue samples were collected after 6 weeks. Behavioural parameters were also assessed. Improvement in growth was seen with increasing inclusion of DHA up to a maximum at 10 g kg^?1 inclusion, albeit the response was minor. However, the addition of ARA to the diet reduced the growth response, while the addition of EPA improved the growth response. An improvement in feeding behaviour was also seen with increasing DHA up to a peak at 10 g kg^?1, while those animals fed diets low in DHA showed increasingly cryptic behaviour. With the increasing inclusion of DHA, a range of pathologies were observed, but the addition of an EPA component to the diet limited these pathologies, while the addition of ARA made little improvement and in some cases exacerbated the pathologies.     

Feed intake, growth and nutrient utilization in Atlantic halibut (Hippoglossus hippoglossus) fed diets containing a bacterial protein meal

Triplicate groups of Atlantic halibut were fed diets containing 0%, 9% or 18% of a bacterial protein meal (BPM) produced from natural gas in a 9‐week trial. Growth rates, relative feed intake, feed efficiency ratio and retention of all indispensable amino acids were significantly lower in fish fed the 18% BPM diets than in those fed the 0% and 9% BPM diets. There were no significant treatment effects on urea levels in plasma, liver or muscle, or in uric acid levels in plasma. The hepatosomatic index was lowest in fish fed the 18% BPM diet. Although the concentration of copper, an element abundant in BPM, increased in the liver as dietary BPM level increased, the total copper content in liver decreased. Fish fed the 0% and 9% BPM diets had a higher degree of supranuclear vacuolization of pyloric caeca and mid‐intestine epithelia compared with fish fed the 18% BPM diet. In conclusion, the halibut fed the 9% BPM diet performed equally well as the control group regarding growth, feed intake and feed efficiency ratio, whereas performance was reduced in the fish fed the 18% BPM diet.