The attractive effects of amino acids and some classical substances on grass carp (Ctenopharyngodon idellus)

Inclusion Effect of Various Levels of Jack Mackerel Meal in Olive Flounder (Paralichthys olivaceus) Diets Substituting 50% Fish Meal with Duck By-Product Meal on Growth and Feed Utilization

This experiment was performed to evaluate the inclusion impact of various levels of jack mackerel meal (JMM) in olive flounder (P. olivaceus) feeds substituting 50% FM by duck by-product meal (DBM) on growth, feed availability, and economic efficiency. Seven experimental diets were prepared. The control (Con) diet contained 60% FM. Fifty percent FM in the Con diet was substituted with DBM, and then the graded levels (0%, 10%, 20%, 30%, 40%, and 50%) of JMM were added instead of FM, named the DJ0, DJ10, DJ20, DJ30, DJ40, and DJ50 diets, respectively. All feeds were assigned to triplicate fish groups. At the end of 56 days' feeding, fish fed the DJ40 and DJ50 diets exhibited comparable weight gain and specific growth rate to fish fed the Con diet. Higher feed consumption was observed in fish fed the Con, DJ40, and DJ50 diets compared to fish fed the DJ0 and DJ10 diets. Lower feed conversion ratio was observed in fish fed the Con diet compared to fish fed the DJ0, DJ10, DJ20, and DJ30 diets. Furthermore, the DJ50 diet led to the highest economic profit index (EPI). In conclusion, inclusion of 50% JMM in the olive flounder diet replacing 50% FM with DBM seems to be the most recommendable dietary treatment based on growth and feed consumption of olive flounder and EPI.

Understanding olfactory and behavioural responses to dietary cues in age-1 lake sturgeon Acipenser fulvescens

Detection of environmental cues is essential for all vertebrates and is typically established by the olfactory epithelium and olfactory sensory neurons (OSNs). In fishes, microvillous and ciliated OSNs are the principal types, typically detecting amino acids and bile salts, respectively. Activation of OSN receptors by specific ligands initiate downstream signal processing often leading to behavioural responses. In this study we used electrophysiological and behavioural techniques to evaluate olfactory detection and behaviour in juvenile lake sturgeon Acipenser fulvescens in response to hatchery- and natural dietary cues. We hypothesized that electro-olfactogram (EOG) and behavioural responses would be dependent on diet type. We predicted that inhibition of the phospholipase C/inositol 1,4,5-triphosphate (PLC/IP3) secondary transduction pathway would reduce EOG responses to dietary cues and, inhibition of the adenylyl cyclase/adenosine 3,5-cyclic monophosphate (cAMP) pathway, would have no effect. Furthermore, we predicted a strong EOG response would be manifested in a change in behaviour. We observed that both the PLC/IP3 and cAMP pathways were significantly involved in the detection of dietary cues. However, EOG responses did not manifest to behavioural responses, although the foraging activity to the hatchery cue was significantly greater compared to the control. Our results support the notion that lake sturgeon raised in a hatchery and fed a commercial pelleted diet may become accustomed to it prior to release into the wild. Further, this study suggests that, in conservation aquaculture settings, lake sturgeon should be exposed to natural dietary cues prior to release as one strategy to promote food recognition.