Abstract
Two 4-week tank feeding trials were conducted with market size (1.5 kg+) mulloway (Argyrosomus japonicus) to evaluate current commercial grow-out feeding practices related to short-term fasting. Growth performance, feed intake and efficiency were evaluated in seawater during spring 2013 (September-October, water temperature 18.22- 21.97°C) and autumn 2014 (May-June, 19.42-23.0°C). Mulloway fed continuously in spring on a 6 day on - 1 day off rotation, had the highest condition index (1.12), grew significantly (P < 0.05) faster (SGR 0.35% day-1) and had better feed efficiency (FCE 76.97%) than fish subjected to two different repetitive periods of fasting and satiation refeeding (1 day on -1 day off, SGR 0.24% day-1, FCE 62.57%; 2 days on - 1 day off, SGR 0.22% day-1, FCE 58.24%); despite these fish exhibiting hyperphagia. Feeding vigour and appetite was more pronounced in the 1 day on - 1 day off than the 2 day on - 1 day off rotation. In autumn mulloway fed 5 days week-1 had the lowest final weight (1.63 kg), grew significantly slower (SGR 0.26% day-1), had poorer feed conversion (FCR 1.63) and condition (K 1.06) than fish fed 7 days week-1 (final weight 1.74 kg; SGR 0.44% day-1; FCR 1.3, K 1.09). The results of this study suggest that two-year-old mulloway do best under a constant feeding frequency while management actions, such as short-term fasting and not feeding on the weekend, will have a negative impact on fish growth and condition.
Highlights
Feeding is one of the most important activities in fish farming and comprises the choice of feed, control of ration size and temporal and spatial delivery to the fish [1]
Two-year-old mulloway were collected from a commercial fish farm and transported by road (1.5 hours) in an oxygenated 900 L transport tank at a density of 75 kg m-3 to holding tanks at the National Marine Science Centre (NMSC), Charlesworth Bay, Coffs Harbour
Mulloway that were fed more consistently (6 days on - 1 day off), had the highest condition index (1.12), grew significantly (P < 0.05) faster (SGR 0.35% day-1) and had better feed efficiency (FCE 76.97%) than fish exposed to the two different repetitive periods of fasting and satiation re-feeding (1 day on - 1 day off, SGR 0.24% day-1, FCE 62.57%; 2 days on - 1 day off, SGR 0.22% day-1, FCE 58.24%) (Table 3)
Summary
Feeding is one of the most important activities in fish farming and comprises the choice of feed, control of ration size and temporal and spatial delivery to the fish [1]. Determining the optimal feeding frequency of farmed species, has been difficult, as this can vary with fish species, size and culture system [4]. Smaller fish (fry and fingerlings) are fed smaller meals with greater frequency while once day-1 is usually sufficient for larger market-size fish. Some species, such as rainbow trout (Oncorhynchus mykiss) grow faster when fed four times day-1 compared with twice while the estuary grouper (Epinephelus tauvina) grow faster and show improved FCRs when fed every other day, compared to once day-1 or several times day-1. In post-smolt Atlantic salmon (Salmo salar) there was little or no effect on average growth with increased feeding frequency [5,6,7]
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