Department of Ichthyology, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia.
Laboratory for Behaviour of Lower Vertebrates, Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia.
J Fish Biol. 2021 May;98(5):1385-1400. doi: 10.1111/jfb.14675. Epub 2021 Feb 2.
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 (r = 0.27; P > 0.05). Palatability of sugars for O. niloticus and their sweetness for humans did not correlate as well (r = 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.
鱼类的味觉偏好主要见于肉食性物种，而草食性消费者在这类研究中很少被使用。本研究的主要目的是评估草食性非洲丽鱼，尼罗河罗非鱼 Oreochromis niloticus 的味觉偏好。在实验室环境中，评估了广泛使用的味觉物质（被认为对人类来说是甜、酸、苦和咸的四种味觉物质——蔗糖、柠檬酸、氯化钙和氯化钠；21 种游离 L-氨基酸；12 种糖和人工甜味剂 Na-糖精；0.1-0.0001 M）的适口性。在每次试验中，单独向鱼提供一种用物质调味的标准琼脂丸。记录丸的消耗、抓取次数和在最终吞下或拒绝丸之前的保留时间。总的来说，38 种物质中有 21 种是可口的，而其他物质并没有改变丸的消耗，与空白丸相比。柠檬酸、L-半胱氨酸、L-正缬氨酸、L-异亮氨酸、L-缬氨酸、Na-糖精和 D-山梨醇的丸的消耗>85%的试验中。氨基酸的味觉吸引力具有高度的物种特异性，与比较的 19 种物种的营养类别无关。此外，它与尼罗罗非鱼的饮食定量需求也没有相关性（r=0.27；P>0.05）。尼罗罗非鱼对糖的适口性与其对人类的甜度也没有相关性（r=0.21；P>0.05）；尽管如此，Na-糖精对尼罗罗非鱼和人类来说都具有最吸引人的味道。当 L-半胱氨酸的浓度降低到 0.01 M 和 L-正缬氨酸的浓度降低到 0.001 M 时（分别低于每丸 242.3μg 和 23.4μg），最可口的氨基酸就失去了效果。单丸抓取是尼罗罗非鱼摄食行为的特征（>95%的试验），这种模式可能与该物种的社会生活方式有关。鱼平均花费 4-8 秒用于对丸的可食性进行口部感觉评估。保留时间与物质的适口性相关，在最终吞下丸的试验中明显延长。这表明在吞下食物之前对食物进行长时间的口部感觉评估可以提供可靠和准确的感官评估，从而降低摄入不适当食物的可能性。
