Sleep is a conspicuous and prominent behavioural state found across the animal kingdom (Ungurean, van der Meij, Rattenborg, & Lesku, 2020). It is often associated with behavioural correlates, such as quiescence in a species-specific posture, which is rapidly reversible to wakefulness, and a decrease of awareness of the local environment resulting in an increased arousal threshold. Sleep is also regulated by two processes: (a) homeostasis, whereby sleep loss increases sleep need, causing animals to sleep more and/or more intensely (Tobler, 2011), and (b) a circadian process, whereby an internal clock is entrained by environmental zeitgebers, such as 24-hr natural light-dark cycles, to influence the adaptive timing of sleep and wakefulness (Kazimi & Cahill, 1999). In many organisms, once a circadian clock is set, circadian rhythms are (largely) maintained even under constant conditions, such as constant light or dark (Falcon, Besseau, Sauzet, & Boeuf, 2007). These behavioural features of sleep can be used to test for the presence (or absence) of sleep in a diversity of animals in a comparative framework aimed at understand-
The nursery culture of bivalves typically relies on the feeding of costly live microalgae, while the use of natural sources of phytoplankton for feed is uncertain due to their variable quality and abundance. Replacement diets have been applied in bivalve nursery culture to replace live microalgae with varying success. This study investigated the potential use of two concentrated microalgal diets at a range of levels of substitution with live microalgae. Shellfish Diet 1800® (called SD) and LPB™ Frozen Shellfish Diet® (called LPB) were fed to juvenile green-lipped mussels (Perna canaliculus) at five levels of substitution for live microalgae (i.e., 0, 25, 50, 75, and 100%) for 27 days. The mortality of mussels fed with 100% LPB replacement was significantly higher than the mortality of mussels fed at the lower levels of replacement, i.e., 0 and 25%. The overall final size of spat tended to decrease with the increasing level replacement of live microalgae. Proximate analysis (i.e., crude ash-free dry weight, crude protein, crude lipid, and carbohydrate) showed that only the proportion of carbohydrate content of spat was influenced by feeding treatments, with the mean total carbohydrate content of mussels tending to decrease with increasing levels of replacement of live microalgae. The results indicate that both concentrated microalgal feeds (SD and LPB) are effective at replacing live microalgae by up to 50% without compromising the survival and nutritional profile (AFDW, protein, lipid, and carbohydrate content) of juvenile green-lipped mussels and are therefore a useful resource for improving the efficiency of production.
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