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In the cultivation of barramundi Lates calcarifer, one of the key factors is developing new commercial feeds that are nutritionally adequate and attractive to fish. The sensory quality of feeds can be improved by taste stimulants. The aim of the present study is to examine the taste attractiveness of 21 free L-amino acids and 4 basic taste substances (0.1–0.001 M). The feeding behavior that accompanied the orosensory testing of feed is also studied. Agar pellets flavored with each taste substance were individually offered to barramundi juveniles (5–9 cm, 4–10 g). Citric acid, cysteine, and alanine were palatable; sucrose and 7 amino acids had an aversive taste; sodium chloride, calcium chloride, and 12 amino acids did not influence the consumption of pellets. Taste preferences for amino acids are positively correlated in 6 out of 21 fish species, which confirms high species specificity of taste preferences in fishes. Barramundi often make repeated grasps and rejections of pellets regardless of their palatability, which led to the destruction of pellets in up to 50% of trials. When swallowing, fish retain pellets several times longer, and pellet fragmentation occurs more often, than in the case of final refusal of pellets. The data presented here can be used to improve the cultivation of barramundi. [ABSTRACT FROM AUTHOR]

In the cultivation of barramundi Lates calcarifer, one of the key factors is developing new commercial feeds that are nutritionally adequate and attractive to fish. The sensory quality of feeds can be improved by taste stimulants. The aim of the present study is to examine the taste attractiveness of 21 free L-amino acids and 4 basic taste substances (0.1–0.001 M). The feeding behavior that accompanied the orosensory testing of feed is also studied. Agar pellets flavored with each taste substance were individually offered to barramundi juveniles (5–9 cm, 4–10 g). Citric acid, cysteine, and alanine were palatable; sucrose and 7 amino acids had an aversive taste; sodium chloride, calcium chloride, and 12 amino acids did not influence the consumption of pellets. Taste preferences for amino acids are positively correlated in 6 out of 21 fish species, which confirms high species specificity of taste preferences in fishes. Barramundi often make repeated grasps and rejections of pellets regardless of their palatability, which led to the destruction of pellets in up to 50% of trials. When swallowing, fish retain pellets several times longer, and pellet fragmentation occurs more often, than in the case of final refusal of pellets. The data presented here can be used to improve the cultivation of barramundi.

Taste preferences in fishes are known mainly for carnivorous species, whereas herbivorous consumers were rarely used in such studies. The main goal of the present study was to evaluate the taste preferences in the herbivorous African cichlid fish, Nile tilapia Oreochromis niloticus. In laboratory settings, the palatability of widely used taste substances (four taste substances that are considered to be sweet, sour, bitter and salty for humans – sucrose, citric acid, calcium chloride and sodium chloride; 21 free L‐amino acids; 12 sugars and artificial sweetener Na‐saccharin; 0.1–0.0001 M) was evaluated. In each trial, a standard agar pellet flavoured with a substance was offered for fish individually. The consumption of pellet, the number of grasps and the retention time before the pellet was finally ingested or rejected were registered. Overall, 21 of 38 substances were palatable, whereas other substances did not shift consumption of pellets in relation to blank pellets. Pellets containing citric acid, L‐cysteine, L‐norvaline, L‐isoleucine, L‐valine, Na‐saccharin and D‐sorbitol were consumed in >85% of trials. Taste attractiveness of amino acids was highly species‐specific and was not associated with the trophic category of the 19 species compared. Moreover, it did not correlate with dietary quantitative requirements of Nile tilapia (rs = 0.27; P > 0.05). Palatability of sugars for O. niloticus and their sweetness for humans did not correlate as well (rs = 0.21; P > 0.05); nonetheless, Na‐saccharin has the most attractive taste for both O. niloticus and humans. The most palatable amino acids lost their effect if the concentration was lowered to 0.01 M for L‐cysteine and 0.001 M for L‐norvaline (lower than 242.3 μg and 23.4 μg per a pellet, respectively). Single pellet grasp was characteristic of O. niloticus feeding behaviour (>95% of trials), and this pattern may be related to the social lifestyle of this species. Fish spent 4–8 s on average for orosensory evaluation of pellet edibility. The retention time correlated with the palatability of substances and was significantly longer in trials that ended up with pellet swallowing. It is suggested that prolonged orosensory evaluation of food before swallowing provides a reliable and accurate sensory evaluation, which, in turn, can reduce the probability that inadequate food will be consumed. [ABSTRACT FROM AUTHOR]

Comparative study of the taste attractiveness of different aquatic invertebrates (daphnids Daphnia longispina and D. pulex, larvae of Chironomidae, whirligig Gyrinus marinus, water skaters Gerris spp.) and plants (duckweed Lemna minor, filamentous alga Cladophora sp.) for roach Rutilus rutilus, bitterling Rhodeus sericeus amarus, and rainbow trout Oncorhynchus mykiss has been performed. Roach's taste preferences for agar-agar pellets, containing the aqueous extracts of the organisms under study, varies from maximum (daphnids, filamentous alga, larvae of chironomids) to minimum (duckweed) or it can be absent (whirligig). Different taste preferences to pellets containing the extracts of aquatic organisms has been also found in bitterling (daphnids, larvae of chironomids, water skaters) but not in rainbow trout (daphnids, water skaters). It has been suggested that whirligigs and water skaters do not contain any deterrent substances ensuring chemical defense from predators. It has been demonstrated that intraoral gustatory reception of food items follows two alternative behavioral stereotypes that are different from each other in the time during which food items are retained in the oral cavity and the number of manipulations (subsequent grasps of a food item) during the perception process. We discuss the importance of gustatory reception as the major sensory mechanism that ensures feeding selectivity of fish and decreases interspecific competition over food. [ABSTRACT FROM AUTHOR]