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Text|Broken Boat Han
Editor|Broken Boat Han
preface
In recent years, more and more attention has been paid to the influence of environmental factors on the cognitive ability and growth performance of fish.
As an important economic fish, black stone fish has a wide application value in fishery and aquaculture industry, but with the expansion of breeding scale, the cognitive ability and growth performance of black stone fish face new challenges.
Environmental enrichment, as a possible management method, is thought to promote cognitive development and growth improvement in black stonefish, but its effect mechanism still needs further study.
There is also a focus on environmental changes and stimuli, which have been shown to have positive effects on cognition and growth in other fish studies.
Different methods of environmental enrichment, such as providing diverse feeds and introducing structured environments, can stimulate intellectual curiosity and exploratory behavior in fish, which may improve their cognitive abilities.
In addition, environmental enrichment may also affect the growth performance of blackstone fish by providing more exercise space and stimulation, and promote its growth and development.
Effects of environmental enrichment on fish
In the juvenile stage, fish are prone to starvation and predation, thus exacerbating their mortality, and many researchers, attribute the high mortality of released fish, to juveniles raised in captivity, may not have sufficient capacity to survive in the wild, for example, modern industrial aquaculture systems for commercial farming tend to maintain high population density.
The living environment is not as complex and uncertain as the natural environment, and many factors may lead to cognitive decline and abnormal behavioral characteristics of fish, ultimately leading to low survival after release, and an important means to improve this situation is environmental enrichment.
Studies have shown that complex environments can improve cognitive abilities and play an important role in shaping fish's nervous systems, with two of the most important factors being the heterogeneity of the physical environment and social complexity.
Where social interaction can provide neural stimulation and increase the number of synaptic connections and neurogenesis, thereby facilitating learning, the complexity of the physical environment provides similar effects to social enrichment.
Spatial cognition is especially important for fish, which involves perception and spatial cues, and the ability to retrieve this information and use learning and memory to help them modify their behavior to find a location or follow a specific route, so cognitive ability is especially important for the survival of fish that inhabit complex and variable environments.
In general, cognition can be defined as animal behavior, as well as physiological changes, poor environments can impair fish's cognitive abilities, but the impact of environmental complexity on fish cognition, both in terms of behavioral and molecular mechanisms.
Much remains unknown, and in order to better understand this relationship, it is important to study how the living environment of fish affects their cognitive abilities through cognitive assessment devices and the detection of relevant indicators.
Among various behavioral assessment methods, the maze test is widely used to assess the cognitive abilities of animals, and among the various types of maze tests, the T maze is an effective method that is widely used to assess the cognitive abilities of rodents and in recent years has also been used to assess the cognitive abilities of fish.
There are also neuroscientists who are particularly interested in the molecular mechanisms of neuroplasticity, with a particular focus on the neurotrophic factor family, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF).
As a member of the neurotrophic factor family and playing an important role in neuroplasticity, NGF was originally described as a neuronal survival and growth factor in the synthesis of innervation density, neurotransmitters, and neuropeptides.
BDNF plays an important role in neuroplasticity by shaping and refining synapses and promoting neurogenesis and cell survival, and both NGF and BDNF play a key role in neuronal proliferation, differentiation and synaptic formation.
Studies have found that BDNFmRNA is widely expressed in the brains of 7-day-old zebrafish larvae, suggesting that neurotrophic factors begin to affect the cognitive function of juveniles soon after birth, so they are determined to be closely related to individual learning and cognitive ability.
In addition to cognitive abilities, individual size also tends to affect the predation ability of juveniles and the number of parasites on the body surface, thus affecting their survival.
Similar to other vertebrates, fish growth is also regulated by endocrine, particularly through the growth hormone (GH) insulin-like growth factor-1 (IGF-1) axis, GH is mainly secreted by growth hormone in the pituitary gland.
The release of somatostatin (SS) in the hypothalamus also plays a role in regulating GH release, while growth hormone released by the pituitary gland enters the blood circulation.
Binding to hepatic GH receptors, stimulating the synthesis and release of IGF-1 is a 7.5 kDa single-chain polypeptide responsible for cell differentiation and proliferation, and promotes individual growth by stimulating the associated processes of bone growth.
Widely distributed in coastal areas of northern China, Japan and South Korea, blackstone is an important species for population growth due to its fishery value, but its resources are seriously declining due to overfishing.
The black stonefish usually inhabits rocky and seagrassed areas, where it needs strong adaptations to cope with complex environmental changes and competition from other species with similar habits.
In addition to this, the black stonefish exhibits strong plasticity and adaptability, allowing it to adapt to a variety of natural habitats, so this species is a suitable species to study the cognitive abilities of fish.
2. Materials and methods
1. Design of experiments
Juvenile blackstonefish were taken from the Wendenghaihe Hatchery, a commercial hatchery in Weihai, Shandong, China, and were used to experimental conditions in an indoor tank for 15 days before the experiment began.
Fish with similar initial body length and weight, without body surface damage, are selected for experiments, and the experimental fish are cultured in a strengthened glass tank, using gas stones for continuous oxygen supply to maintain the dissolved oxygen content of the water.
The water temperature gradually drops from 19 ° C to 13 ° C, the photoperiod follows a natural day and night cycle, the salinity is maintained between 28 and 30, the water level is maintained at 40 cm, and the tank is cleaned 3 times a week to avoid excessive disturbance of the fish, such as oscillations when sucking the bottom for too long.
No contact with other species had been made prior to the start of the experiment, and in the natural environment, their habitats overlapped and sometimes competed.
T maze, left: profile display; Right: Specifications.
2. Group observation
After a 7-week rearing period, 60 fish were selected for the T maze trial, which were divided into twelve tanks and temporarily kept in captivity according to their original sequence.
To reduce stress and familiarize the experimental fish with the device, they are transferred to the device twice a day, 2 h in the morning and 2 h in the afternoon, for a total of three days before the start of the T maze test.
We ensure that each fish gets information about the food supply in the concentration zone as the fish acclimatize to the equipment, and at the end of each experiment, different groups of fish are placed in separate tanks to avoid mixing with other fish.
The T maze test lasted for a week, the fish were fasted to maintain food motility, and each treatment group ran the experiment simultaneously, and after a 15-minute acclimatization period, the fish were released into the starting area.
The time required to reach the habitat for foraging or settlement for at least 5 min was recorded, individuals who failed to reach the habitat within 15 min were recorded for 900 seconds, the photoperiod followed a natural day-night cycle, and the order of measurement varied each day was different to avoid the effects of light intensity and time variations on each group.
The experiment was recorded using a camera placed at a distance from the tank to avoid disturbing the fish, and previous studies have shown that many fish have the ability to learn and integrate information, and the processing of this information is a complex process.
3. Results
The most important region of these complex neural processes in the brain is the dorsolateral telencephalon (DI), which is considered a functional homolog of the mammalian hippocampus, and selective BDNF is the most expressed member of the nerve growth factor family and plays an important role in neuroplasticity.
As a member of the neurotrophic factor family, another factor NGF is also the earliest and most thoroughly studied factor, playing an important role in regulating the development, differentiation, growth, regeneration and expression of central and peripheral neuronal functional characteristics.
Studies have shown that environmental enrichment affects the expression of some cognitive-related factors and genes in fish brains, and the results show that fish living in complex environments for a long time have stronger learning and cognitive abilities, which may be related to the environmental "stimulation" of their brains.
This stimulation promotes upregulation of BDNF and NGF and enhances neuroplasticity, which is essential for individual survival, and we selected only two members of the cognitive-related neurotrophic factor family, and subsequent studies should consider other cognitive-related factors.
These include how increased levels of BDNF and NGF lead to cognitive improvement, whether other factors interact with it, and the primary and secondary roles of different factors in the cognitive enhancement process.
It is worth noting that more complex environments may cause stronger stimulation, which is conducive to increasing cognitive flexibility, and the results can provide a reference for improving the proliferation efficiency of Schleglis.
Individual size is also one of the most fundamental key factors for fish survival, and in previous studies of salmonids, the size of individuals in salmonization affected their ability to adapt to seawater.
Comparison of the effects of growth performance
Through the analysis of growth data after one week of rearing, it was found that habitat enrichment and social enrichment had an impact on juvenile weight, body length, specific growth rate and weight gain rate.
Interestingly, by following up the samples to test three indicators related to growth performance, we found that GH and SS levels in the brains of experimental fish under different treatments differed significantly from IGF-1 levels in visceral mass.
GH and IGF-49 were significantly higher in the enrichment group than in the control group, and SS was significantly lower than in the control group, with opposite growth performance, and from subsequent video analysis, we believe that the reason for this phenomenon is as follows: although the feed volume per tank during the culture period is the same.
However, due to the complex structure of the fish tank in the habitat enrichment treatment group, some of the bait fell into the structure and other places that were difficult for experimental fish to find, and as a result, the fish in the habitat enrichment treatment group ate less than the individuals in the other treatment group, resulting in growth differences, and similar phenomena were found in previous studies.
Starvation can significantly increase plasma GH concentrations in salmonidae and pituitary GHmRNA, and refeeding of hungry fish can lead to increased liver IGF-I concentrations and IGF-51mRNA, and hunger, in addition to affecting growth performance, can also affect fish behavior, and even briefly affect their personality.
Personality includes courage, exploration, initiative, etc., changes in the external environment, sometimes affect the difference in personality indicators between individuals in the population, leading to behavioral differences, which may have an impact on the maze experiment.
On the other hand, due to the close habitat range and living habits of Haemophilus otakii and Haemophilus Shlegley, the presence of Haemophilus otakii may cause "inhibition" on Haemophilus otakii.
Previous studies have shown that competition and stress affect fish physiology and personality behavior, but we have not explored whether this "inhibition" also affects the behavior of experimental fish, so follow-up studies should pay more attention to the relationship between personality behavior, learning cognitive ability, and stress.
Since the levels of hormones that regulate growth in the enrichment group are higher than in the control group, we believe that experimental fish will exhibit compensatory growth in subsequent processes in this context.
In order to avoid this phenomenon and improve the utilization rate of food, attention should be paid to the location of structures and the selection of species in subsequent studies of environmental enrichment.
Avoid reducing food utilization, and the choice of food type and feeding style can also be improved, such as small and frequent feeding, to avoid food waste and impact on fish growth.
conclusion
Compared with the control group, the levels of BDNF and NGF in the habitat group and the social enrichment group were up-regulated, and the two enrichment methods had a significant interaction on NGF, which may be due to the complexity of the living environment and the stimulation of cognitive processes such as learning and memory.
At the same time, the results of behavioral evaluation were consistent with them, and in the T maze experiment, both the habitat group and the social enrichment group performed better in the T maze, and the time required to find the endpoint within 7 weeks was shorter than that of the control group, and we believe that these two enrichment methods improved the learning and cognitive ability of the experimental fish.
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