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.     

Evaluation of Yellow Lupin Lupinus luteus Meal as an Alternative Protein Resource in Diets for Sea-Cage Reared Rainbow Trout Oncorhynchus mykiss

The performance of sea-water reared rainbow trout Oncorhynchus mykiss fed three isonitrogenous and iso-energetic diets based on either fishmeal, solvent-extracted soybean meal or yellow lupin ( L luteus cv. Wodjil) kernel meal was evaluated. Over the course of a 10-wk study, the fastest growing fish were those fed the diet containing 50% yellow lupin kernel meal (YLM), which grew from 83.6 ± 0.7 g to 322.8 ± 3.2 g (mean ± SEM). This was not significantly faster than growth of fish fed the diet based on 50% solvent-extracted soybean meal (SBM), though it was significantly ( P < 0.05) faster than the growth of fish fed the fishmeal based diet (FSM). Growth of fish fed the experimental diets was comparable to growth of fish fed a range of commercial diets as a reference. Survival of fish fed the FSM diet was poorest of all the treatments (47.4%), though this was only significantly poorer than that of fish fed the YLM diet (88.9%). Feed intake was highest by fish fed the YLM diet (5.58 g/d) and lowest for fish fed the FSM diet (336 g/d). Reasons for these differences in feed intake were not clear, though they may be related to different levels of buoyancy and palatability among the diets. Feed conversion rate (FCR) was consistent between treatments at about 1.6:1, though given that this study was a sea-cage based experiment it is likely that considerable unaccounted feed losses occurred, thereby inflating the feed conversion value. Sensory evaluation of fish fed the three test treatments showed no overall difference in the acceptability of the fish, further supporting that solvent-extracted soybean meal and yellow lupin kernel meal both have considerable potential to replace fishmeal as a protein resource in diets for rainbow trout.