Peer Review Science July ’17

Welcome to July’s edition of Zoo Science for Keepers and Aquarists. Lots of new science, from marble gobies, investigating the effect of urban sounds, to Elephant management – and more!


Stieglitz J.D, Hoenig R.H, Kloeblen S., Tudela C.E, Grosell M., Benetti D.D, (2017) Capture, transport, prophylaxis, acclimation, and continuous spawning of Mahi-mahi (Coryphaena hippurus) in captivity, Aquaculture, Volume 479:1-6

Abstract:Successful culture of marine fish relies upon availability of high quality fertilized eggs obtained from broodstock. However, some of the most critical aspects of obtaining such eggs are often overlooked. These aspects include the capture, transport, acclimation, and spawning of sexually mature wild-caught fish. Mahi-mahi (Coryphaena hippurus), also known as dolphinfish, have been identified as one of the most promising candidate species for development of warm-water marine finfish aquaculture due to their high growth rate, market presence, and global distribution. In addition, mahi-mahi have proven to be a useful model species for physiology and environmental toxicology research, specifically in studies examining tropical and subtropical pelagic teleosts. One of the keys to aquaculture development of this species is the ability to obtain year-round production of fertilized embryos. This study documents the technical methods utilized to reach a point of consistent mahi-mahi egg production year-round, while also detailing the live transport tank and land-based spawning tank design, implementation, and operation. Following three different groups of wild-caught mahi-mahi broodstock from the point of capture throughout their lifespan, this study provides novel information on growth, survival, and spawning of this species in captivity. Results from this research have allowed for significant new insights into the effects of a variety of environmental stressors on the early life stages of this species. Furthermore, the ability to maintain consistent spawning populations of mahi-mahi in captivity has allowed for reliable and consistent production of fully-weaned fingerlings of this species, thereby resolving one of the key industry bottlenecks that has been limiting expansion of mahi-mahi commercial-scale aquaculture.


Andrade-Porto S.M, Gusmão Affonso E., Kochhann D., Oliveira Malta J.C, Roque R., Ono E.A, Oliveira Araújo C.S, Tavares-Dias M., (2017) Antiparasitic efficacy and blood effects of formalin on Arapaima gigas (Pisces: Arapaimidae), Aquaculture, Volume 479: 38-44 

Abstract:  This study evaluated the in vitro and in vivo antiparasitic efficacy of formalin against Dawestrema cycloancistrium, the effects on the physiological response of Arapaima gigas and the residual action on fish muscle after 96 h of exposure. As regards the in vitro assay, 0, 22, 44, 66, 88, 110, 330, 660 and 880 mg L− 1 formalin were tested. After 1 h of exposure to 660 and 880 mg L− 1 formalin, there was a 100% mortality of D. cycloancistrium as well as after 2 h of exposure at 330 and 110 mg L− 1 and 3 h of exposure at 44, 66 and 88 mg L− 1. Concerning the in vivo test, when fish were exposed to formalin at 0, 220, 330, 440 and 550 mg L− 1, there was 100% survival at all concentrations and exposure times evaluated. Baths of 1 h with 440 and 550 mg L− 1 formalin showed 93.3% and 99.3% efficacy respectively. However, the baths of 12 h with 55 and 66 mg L− 1 formalin had the efficacy of 44.5% and 55.5% respectively. In 1 h baths with 220, 330, 440 and 550 mg L− 1 formalin, hematocrit, hemoglobin, number of total erythrocytes, mean corpuscular volume, mean corpuscular hemoglobin concentration, mean corpuscular hemoglobin, plasma glucose levels, cortisol, total proteins, chloride, calcium, sodium, potassium and magnesium of the fish presented no differences in relation to the control values. However, in baths of 12 h with 33, 44, 55 and 66 mg L− 1 formalin, there was a decrease in hematocrit, plasma levels of calcium and chloride, and increased levels of glucose and cortisol, depending on the concentration of formalin used. In the fish muscle, the formalin residue decreased after 96 h in all concentrations and periods evaluated, returning to values close to the control ones. The results indicate that formalin had its efficacy successfully proved in the treatment against D. cycloancistrium at higher concentrations such as 440 and 550 mg L− 1 formalin and shorter exposure time (1 h) without compromising fish homeostasis and consumer food safety.Statement of relevanceThe manuscript represents original research on use of formalin in vitro and in vivo for treating infection by monogenoidean Dawestrema cycloancistrium in Arapaima gigas, the giant fish from Amazon. In the fish, muscle the residue levels of formalin after exposure was also investigated. Formalin have efficacy in the treatment against D. cycloancistrium at higher concentrations (440 and 550 mg.L− 1) of formalin and shorter exposure time (1 h) and without compromising A. gigas homeostasis and consumer food safety.

Aquaculture Reports -May 2017 Volume 6

Bolasina S.N, de Azevedo A., Petry A.C,(2017) Comparative efficacy of benzocaine, tricaine methanesulfonate and eugenol as anesthetic agents in the guppy Poecilia vivipara, Aquaculture Reports, 6: 56-60,  

Abstract: The aim of this study was to evaluate the anesthetic efficacy and determine the lowest effective concentration in the guppy, Poecilia vivipara. Fishes were exposed to benzocaine, tricaine methanesulfonate and eugenol at three different concentrations. After induction, they were transferred to an aquarium free of anesthetic for evaluating their recovery time. At the lowest concentration of the three anesthetics (50 mg L−1), fish did not reach complete induction. Time to accomplish a light sedation stage was significantly negative-related with concentration using tricaine (145 ± 13.4 s with 50 mg L−1 to 4.7 ± 0.7 s with 200 mg L−1) and benzocaine (152.8 ± 13 s with 50 mg L−1 to 4.0 ± 0.9 s with 200 mg L−1). For eugenol, significant differences were found between the lowest concentration, 50 mg L−1 (241 ± 57.6 s) with 100 mg L−1 (13.3 ± 3.9 s) and 200 mg L−1 (9.5 ± 2.6 s). Recovery times were significantly longer (P < 0.05) with the increase of eugenol concentration from 100 mg L−1 to 200 mg L−1, with no differences found between the different concentrations of benzocaine and tricaine. Complete induction times were significantly greater (P < 0.05) when using eugenol comparing with the other two anesthetic agents in fish exposed at the highest concentrations (200 mg L−1). This parameter showed a great dispersion when using eugenol at this concentration. Three fish exposed to 200 mg L−1 of eugenol did not recovered from the anesthetic after 180 s and presented ventilatory failure. Significantly shorter recovery times (P < 0.05) were found using tricaine comparing with eugenol (120 ± 24.8 s and 163.5 ± 57.1 s, respectively) at the higher concentration (200 mg L−1). The optimum dose rates of benzocaine and tricaine for induction within the efficacy criteria stated in this study was 200 mg L−1. It can be concluded these anesthetics are the more effective ones, being benzocaine more economically affordable for large-scale use on handling P. vivipara.

Cirino P., Ciaravolo M., Paglialonga A., Toscano A., (2017) Long-term maintenance of the sea urchin Paracentrotus lividus in culture, Aquaculture Reports, 7:27-3

Abstract: The common sea urchin Paracentrotus lividus (Lamarck, 1816) is an important commercial species in the Mediterranean Sea for the consumption of its gonads (roe). This species has also long been used as an animal model in developmental biology and as an indicator in the assessment of environmental quality. In recent decades, the exploitation of this marine resource has become increasingly intensive, causing the depletion of wild stocks. The ripple effect observed in the laboratory use of this species has been the growing difficulty in finding valiant mature animals in the wild. We focused on the long-term maintenance of wild P. lividus and on the essential question of diet to maintain the animals and improve gonad development. The use of practical ration blocks which are nutrient-rich and show stability, easy storage and handling, resulted reduction in labour requirement and time for feeding streamlining the feeding practice. A significantly higher gonad production and a prolonged period of reproduction were obtained compared to wild caught individuals over the same period of time.

Zoo Science July

Zoo Biology – In Press articles

Helena Stokes, Vijitha Perera, Nilmini Jayasena and Ayona Silva-Fletcher. Nocturnal behavior of orphaned Asian elephant (Elephas maximus) calves in Sri Lanka

DOI: 10.1002/zoo.21360

Many animals exhibit circadian variation in behavior; thus, studying nocturnal behavior is important to fully understand species activity patterns. The nocturnal behavior of Asian elephants, and specifically calves, has received little previous study. We carried out observational study of the nocturnal behavior of orphaned Asian elephant calves at three age groups: “infant” (0–24 months), “young juvenile” (25–36 months) and “old juveniles” (over 36 months). Project aims were to build a nocturnal activity budget, to investigate key age differences, and whether calves exhibited synchronous behavior patterns. We carried out focal animal sampling and instantaneous group scan sampling on 34 calves for 18 nights using an infra-red camera. Focal results indicated that calves spent the highest percentage of scans in lying rest (46.2%) and feeding (28.4%). There was no significant difference between lying rest in the three age groups. Calves spent the majority of time within 5 m of their nearest neighbor, with infants remaining in closest proximity to conspecifics compared to older calves. Synchronous behavior could not be proved statistically but two distinct lying rest periods between 2300 and 0100, and 0330 and 0530, were noted. We found that calves spent more time in lying rest than previously observed in adult elephants. Activity patterns observed suggest that the orphaned group behavior is similar to that reported in the wild and captive zoological collections, and appears to be in concordance with “natural” behavior patterns, a defining feature of animal welfare. This research provides valuable data as a preliminary study.


Octavian Craioveanu, Cristina Craioveanu, Vioara Mireşan. Plasticity of thermoregulatory behavior in leopard geckos (Eublepharis macularius, Blyth 1954)

DOI: 10.1002/zoo.21374

Studies on thermoregulation in nocturnal lizards have shown that their thermal regimes are similar to those of diurnal lizards, even though they hide during the daytime and are active mostly at night, when heat sources are very scarce. As a result, nocturnal lizards display an active thermoregulatory behavior consisting of seeking warm shelters to hide during the daytime, using accumulated heat for the nocturnal activity. Based on this information, we hypothesize that when leopard geckos (Eublepharis macularius, Blyth 1954) are presented with the choice of safety in cool shelters or vulnerability in heated open areas, suitable temperature will prevail in importance, i.e. they will trade the advantages provided by the shelter for an exposed, but physiologically necessary heat source. Data on the time juvenile E. macularius spent in shelters, and in open areas along a thermal gradient and under a 12/12 hr photoperiod, from eight individuals confirmed our hypothesis. We found that, not only did they select heat sources over shelters, but, along with the light/dark cycle, temperature may also represent a cue for activity. Additionally we found that substrate moisture plays an important role in shelter preference.


Courtney Collins, Ilse Corkery, Amy Haigh, Sean McKeown, Thomas Quirke, Ruth O’Riordan. The effects of environmental and visitor variables on the behavior of free-ranging ring-tailed lemurs (Lemur catta) in captivity

DOI: 10.1002/zoo.21370  

The effect of the zoo environment on captive animals is an increasingly studied area of zoo research, with visitor effects and exhibit design recognized as two of the factors that can contribute to animal welfare in captivity. It is known that in some situations, visitors may be stressful to zoo-housed primates, and this may be compounded by environmental factors such as the weather, the time of day, and zoo husbandry routines. Exhibit design and proximity of the public are also known to influence behavioral response of primates to visitors; however, there is minimal research on free-ranging zoo animals, even though they are potentially subjected to intense interactions with visitors. The current study explores the effect of the zoo environment, several visitor variables and specific animal–visitor interactions on the behavior of free-ranging ring-tailed lemurs (Lemur catta) at Fota Wildlife Park, Ireland. Data were obtained through scan samples collected over 18 months (n = 12,263) and analyzed using a range of statistical tests, including general estimating equations (GEE). Results demonstrate that the free-ranging lemurs’ behavior at Fota Wildlife Park is affected by season, weather and time of day. Similarities in feeding behavior exist between the free-ranging group and lemurs in the wild when resources are plentiful. Visitor variables had a limited effect on lemur behavior and behavioral diversity level. Lemurs rarely reacted to visitors when specific interactions were considered. Generally, the results indicate that the ring-tailed lemurs in this study have adapted well to the zoo environment and habituated to visitors.

Applying behavior-analytic methodology to the science and practice of environmental enrichment in zoos and aquariums. Alligood, C A, .Dorey, N R, Mehrkam, L. R, Leighty, K. A Zoo Biology v36 (3) P175-185

DOI: 10.1002/zoo.21368

Abstract: Environmental enrichment in zoos and aquariums is often evaluated at two overlapping levels: published research and day-to-day institutional record keeping. Several authors have discussed ongoing challenges with small sample sizes in between-groups zoological research and have cautioned against the inappropriate use of inferential statistics (Shepherdson, , International Zoo Yearbook, 38, 118-124; Shepherdson, Lewis, Carlstead, Bauman, & Perrin, Applied Animal Behaviour Science, 147, 298-277; Swaisgood, , Applied Animal Behaviour Science, 102, 139-162; Swaisgood & Shepherdson, , Zoo Biology, 24, 499-518). Multi-institutional studies are the typically-prescribed solution, but these are expensive and difficult to carry out. Kuhar ( Zoo Biology, 25, 339-352) provided a reminder that inferential statistics are only necessary when one wishes to draw general conclusions at the population level. Because welfare is assessed at the level of the individual animal, we argue that evaluations of enrichment efficacy are often instances in which inferential statistics may be neither necessary nor appropriate. In recent years, there have been calls for the application of behavior-analytic techniques to zoo animal behavior management, including environmental enrichment (e.g., Bloomsmith, Marr, & Maple, , Applied Animal Behaviour Science, 102, 205-222; Tarou & Bashaw, , Applied AnimalBehaviour Science, 102, 189-204). Single-subject (also called single-case, or small-n) designs provide a means of designing evaluations of enrichment efficacy based on an individual’s behavior. We discuss how these designs might apply to research and practice goals at zoos and aquariums, contrast them with standard practices in the field, and give examples of how each could be successfully applied in a zoo or aquarium setting.

Sound at the zoo: Using animal monitoring, sound measurement, and noise reduction in zoo animal management  Orban, David A.; Soltis, Joseph; Perkins, Lori; et al. ZOO BIOLOGY   V: 36 (3)   Pages: 231-236

A clear need for evidence-based animal management in zoos and aquariums has been expressed by industry leaders. Here, we show how individual animal welfare monitoring can be combined with measurement of environmental conditions to inform science-based animal management decisions. Over the last several years, Disney’s Animal Kingdom (R) has been undergoing significant construction and exhibit renovation, warranting institution-wide animal welfare monitoring. Animal care and science staff developed a model that tracked animal keepers’ daily assessments of an animal’s physical health, behavior, and responses to husbandry activity; these data were matched to different external stimuli and environmental conditions, including sound levels. A case study of a female giant anteater and her environment is presented to illustrate how this process worked. Associated with this case, several sound-reducing barriers were tested for efficacy in mitigating sound. Integrating daily animal welfare assessment with environmental monitoring can lead to a better understanding of animals and their sensory environment and positively impact animal welfare.

Does enrichment improve reptile welfare? Leopard geckos (Eublepharis macularius) respond to five types of environmental enrichment Bashaw, Meredith J.; Gibson, Mallory D.; Schowe, Devan M.; et al. APPLIED ANIMAL BEHAVIOUR SCIENCE   V184   Pp: 150-160

Animal welfare is a high priority for pet owners and accredited zoos and aquariums. Current approaches to measuring welfare focus on identifying consensus among behavioral and physiological indicators of positive and negative emotions. Environmental enrichment is a common strategy used to improve the welfare of captive animals. In enrichment programs, knowledge of an animal’s ecology and individual history are applied to modify the animal’s current environment and management to increase environmental complexity, make the environment more functional or natural, and increase behavioral opportunities. While enrichment techniques for primates and large mammals are well-studied, reptile enrichment has received little attention to date despite a few promising studies. In this study, we monitored the responses of 16 leopard geckos to five types of enrichment (Thermal, Feeding, Olfactory, Object, and Visual) using a repeated-measures design. We measured both specific behaviors we expected to change in response to each enrichment type and four behavioral indicators of welfare: exploratory behavior, species-specific behaviors (behavioral thermoregulation and hunting), behavioral diversity, and abnormal repetitive behaviors. We found geckos interacted with all five types of enrichment at above-chance levels (i.e., no 95% Cls for engagement time overlapped with 0 s). Geckos spent more time interacting with Thermal and Feeding enrichment than the other types (F(4,60) = 49.84, p < 0.001). Thermal, Feeding, Olfactory, and Object enrichments (but not Visual enrichment) changed specific relevant behaviors (e.g., Thermal enrichment altered thermoregulatory behaviors, Willc’s lambda = 0.25, F(3,13) = 1339, p < 0.001) and improved behavioral indicators of welfare (e.g., behavioral diversity, Wilks’ lambda = 0.30, F(12,178) = 12.31, p < 0.001). These results suggest that geckos respond to environmental enrichment, that their responses are predictable based on their ecology, and that environmental enrichment improves gecko welfare. As in mammals and birds, enrichments that address behavioral needs (here: thermoregulation and feeding) appear more effective than enrichments that simply provide novel stimuli to increase exploration. The extent to which our results can be generalized to other reptile species awaits further study, but we suggest that enrichment should be more widely used to improve reptile welfare.

Hair plucking, stress, and urinary cortisol among captive bonobos (Pan paniscus) Brand, Colin M.; Boose, Klaree J.; Squires, Erica C.; et al. ZOO BIOLOGY   V35 (5)   Pages: 415-422

Hair plucking has been observed in many captive primate species, including the great apes; however, the etiology of this behavioral pattern is poorly understood. While this behavior has not been reported in wild apes, an ethologically identical behavior in humans, known as trichotillomania, is linked to chronic psychosocial stress and is a predominantly female disorder. This study examines hair plucking (defined here as a rapid jerking away of the hair shaft and follicle by the hand or mouth, often accompanied by inspection and consumption of the hair shaft and follicle) in a captive group of bonobos (N=13) at the Columbus Zoo and Aquarium in Columbus, Ohio. Plucking data were collected using behavior and all-occurrence sampling; 1,450 social and self-directed grooming bouts were recorded during 128hr of observation. Twenty-one percent of all grooming bouts involved at least one instance of plucking. Urine samples (N=55) were collected and analyzed for the stress hormone cortisol. Analyses of urinary cortisol levels showed a significant positive correlation between mean cortisol and self-directed plucking for females (r=0.88, P<0.05) but not for males (r=-0.73, P=0.09). These results demonstrate an association between relative self-directed hair plucking and cortisol among female bonobos. This is the first study to investigate the relationship between hair plucking and cortisol among apes. Overall, these data add to our knowledge of a contemporary issue in captive ape management. Zoo Biol. 35:415-422, 2016. (c) Wiley Periodicals, Inc.

Reproductive Health Assessment of Female Elephants in North American Zoos and Association of Husbandry Practices with Reproductive Dysfunction in African Elephants (Loxodonta africana) Brown, Janine L.; Paris, Stephen; Prado-Oviedo, Natalia A.; et al. PLOS ONE V11  (7)

As part of a multi-institutional study of zoo elephant welfare, we evaluated female elephants managed by zoos accredited by the Association of Zoos and Aquariums and applied epidemiological methods to determine what factors in the zoo environment are associated with reproductive problems, including ovarian acyclicity and hyperprolactinemia. Bi-weekly blood samples were collected from 95 African (Loxodonta africana) and 75 Asian (Elephas maximus) (8-55 years of age) elephants over a 12-month period for analysis of serum progestogens and prolactin. Females were categorized as normal cycling (regular 13- to 17-week cycles), irregular cycling (cycles longer or shorter than normal) or acyclic (baseline progestogens, < 0.1 ng/ml throughout), and having Low/Normal (< 14 or 18 ng/ml) or High (>= 14 or 18 ng/ml) prolactin for Asian and African elephants, respectively. Rates of normal cycling, acyclicity and irregular cycling were 73.2, 22.5 and 4.2% for Asian, and 48.4, 37.9 and 13.7% for African elephants, respectively, all of which differed between species (P < 0.05). For African elephants, univariate assessment found that social isolation decreased and higher enrichment diversity increased the chance a female would cycle normally. The strongest multi-variable models included Age (positive) and Enrichment Diversity (negative) as important factors of acyclicity among African elephants. The Asian elephant data set was not robust enough to support multi-variable analyses of cyclicity status. Additionally, only 3% of Asian elephants were found to be hyperprolactinemic as compared to 28% of Africans, so predictive analyses of prolactin status were conducted on African elephants only. The strongest multi-variable model included Age (positive), Enrichment Diversity (negative), Alternate Feeding Methods (negative) and Social Group Contact (positive) as predictors of hyperprolactinemia. In summary, the incidence of ovarian cycle problems and hyperprolactinemia predominantly affects African elephants, and increases in social stability and feeding and enrichment diversity may have positive influences on hormone status.


Elephant Management in North American Zoos: Environmental Enrichment, Feeding, Exercise, and Training Greco, Brian J.; Meehan, Cheryl L.; Miller, Lance J.; et al PLOS ONE   V11( 7)

The management of African (Loxodonta africana) and Asian (Elephas maximus) elephants in zoos involves a range of practices including feeding, exercise, training, and environmental enrichment. These practices are necessary to meet the elephants’ nutritional, healthcare, and husbandry needs. However, these practices are not standardized, resulting in likely variation among zoos as well as differences in the way they are applied to individual elephants within a zoo. To characterize elephant management in North America, we collected survey data from zoos accredited by the Association of Zoos and Aquariums, developed 26 variables, generated population level descriptive statistics, and analyzed them to identify differences attributable to sex and species. Sixty-seven zoos submitted surveys describing the management of 224 elephants and the training experiences of 227 elephants. Asian elephants spent more time managed (defined as interacting directly with staff) than Africans (mean time managed: Asians = 56.9%; Africans = 48.6%; p<0.001), and managed time increased by 20.2% for every year of age for both species. Enrichment, feeding, and exercise programs were evaluated using diversity indices, with mean scores across zoos in the midrange for these measures. There were an average of 7.2 feedings every 24-hour period, with only 1.2 occurring during the nighttime. Feeding schedules were predictable at 47.5% of zoos. We also calculated the relative use of rewarding and aversive techniques employed during training interactions. The population median was seven on a scale from one (representing only aversive stimuli) to nine (representing only rewarding stimuli). The results of our study provide essential information for understanding management variation that could be relevant to welfare. Furthermore, the variables we created have been used in subsequent elephant welfare analyses.


PEERJ – volume 5

Merechal, L; Levy, X; Meints, K ; Majolo, B.  Experience-based human perception of facial expressions in Barbary macaques (Macaca sylvanus). Article Number: e3413

DOI: 10.7717/peerj.3413

Background. Facial expressions convey key cues of human emotions, and may also be important for interspecies interactions. The universality hypothesis suggests that six basic emotions (anger, disgust, fear, happiness, sadness, and surprise) should be expressed by similar facial expressions in close phylogenetic species such as humans and nonhuman primates. However, some facial expressions have been shown to differ in meaning between humans and nonhuman primates like macaques. This ambiguity in signalling emotion can lead to an increased risk of aggression and injuries for both humans and animals. This raises serious concerns for activities such as wildlife tourism where humans closely interact with wild animals. Understanding what factors (i.e., experience and type of emotion) affect ability to recognise emotional state of nonhuman primates, based on their facial expressions, can enable us to test the validity of the universality hypothesis, as well as reduce the risk of aggression and potential injuries in wildlife tourism.

Discussion. These results do not support the universality hypothesis as exposed and naive participants had difficulties in correctly identifying aggressive, distressed and friendly faces. Exposure to facial expressions improved their correct recognition. In addition, the findings suggest that providing simple exposure to 2D pictures (for example, information signs explaining animals’ facial signalling in zoos or animal parks) is not a sufficient educational tool to reduce tourists’ misinterpretations of macaque emotion. Additional measures, such as keeping a safe distance between tourists and wild animals, as well as reinforcing learning via videos or supervised visits led by expert guides, could reduce such issues and improve both animal welfare and tourist experience.

Applied Animal Behaviour Science

Feeding response of marble goby (Oxyeleotris marmorata) to organic acids, amino acids, sugars and some classical taste substances Leong-Seng Lim, Sian-Kang Jason Lai, Annita Seok-Kian Yong, Rossita Shapawi, Gunzo Kawamura. Applied Animal Behvaiour Science In Press June 2017.


Taste preference of marble goby for various taste substances was determined.

  • L-aspartic acid was the most favorable among the 19 amino acids tested at 0.1 M.
  • All organic acids tested at 0.1 M were highly preferable by the fish.
  • Feed pH may influence the fish taste preferences.
  • Higher ingestion ratio was found in the lower pH of organic acids tested at 0.01 M.


Weaning from live to formulated feeds is a major challenge in the culture of marble goby Oxyeleotris marmorata. It can be solved through dietary supplementation of suitable taste substance as feeding stimulant. However, there is still no information on the suitable feeding stimulant for this species. The present study was conducted to evaluate the feeding response of juvenile O. marmorata to 13 organic acids, 19 amino acids, 5 sugars and 2 classical taste substances in a concentration of 0.1 M. The response was judged through behavioural observations to determine the potential feeding stimulant. Fifty O. marmorata were conditioned to accept agar gel pellet, and then tested with the agar gel pellets that contained each of the taste substances. Pure agar gel pellet was used as the negative control. All agar gel pellets with organic acids were fully ingested by the fish (100%). Among the 19 amino acids tested, aspartic acid attained the highest ingestion ratio (94%) which was significantly different (P < 0.05) from the others. All sugars and classical taste substances were totally rejected (0%) by the fish. The taste preference of O. marmorata for organic acids seemed to be influenced by the feed pH. Strong negative linear correlation (r = −0.828; P < 0.01) was detected between the ingestion ratio and pH of the agar gel pellets when the organic acids were tested at 0.01 M. The ingestion ratio increased when the pH decreased, suggesting that the O. marmorata prefers acidic food. Evidently, all the organic acids and aspartic acid tested were potential feeding stimulants for O. marmorata. In developing weaning diets by using these taste substances, the dietary pH should be monitored as it may be one of the factors that influences the fish taste preference.

Food colour preference of hatchery-reared juveniles of African catfish Clarias gariepinus Gunzo Kawamura, Teodora Uy Bagarinao, Mohamad Faizal Bin Asmad, Leong-Seng Lim. Applied Animal Behvaiour Science in press.


  • The food colour preference of African catfish Clarias gariepinuswas determined among a group of 20 juveniles in a transparent aquarium (whose background colour was varied white, blue, green, red, and black) under natural light in a roofed hatchery.
  • The test food used was diced shrimp flesh dyed blue, green, red, and yellow, with non-dyed natural flesh as the white control.
  • The catfish were presented the food in a pair of different colours at a time.
  • The colour of the food that was first approached and ingested was recorded.
  • Overall juvenile African catfish preferred red and blue coloured food.


Food colour preference is a fundamental aspect of food recognition and has practical application in the formulation of artificial diets and the design of visual baits. Food colour affects growth performance and feed efficiency in captive fishes. This study determined the food colour preference of the juveniles of the African catfish Clarias gariepinus under natural light in a roofed hatchery. A group of 20 juveniles were held in a transparent aquarium whose background colour was made white, blue, green, red, or black. The test food was diced shrimp flesh dyed blue, green, red, and yellow, with non-dyed natural flesh as the white control. In the food colour preference test, the catfish were presented the shrimp flesh in a pair of different colours at a time. The colour of the food that was first approached and ingested, i.e., the first response, was recorded. All the 10 possible food colour pairs were tested against five background colours. Quantitative analysis of the frequency of first response was done by χ2 test and Thurstone’s law of comparative judgment. The juveniles exhibited clear food colour preference that varied with the background colours. Against the black background, the first response was significantly biased to red shrimp flesh. Against the red and blue backgrounds, red and blue shrimp flesh were significantly preferred. Against the white and green backgrounds, no significant color preference was detected. Overall, juvenile African catfish preferred red and blue coloured shrimp flesh. This distinct preference for red and blue food could not be explained by associative learning (brown feed in the hatchery) and seemed innate.


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