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My final paper has been published as a new page at: https://en.wikipedia.org/wiki/Fish_aggression

Fish Aggression Aggression refers to hostile or violent behavior or attitudes toward another, mainly by applying physical force. Evolution on the other hand, is any process of formation or development of something like habit, trait or character in a population from generation to generation. It would be interesting to know how aggression has evolved in fish over time. Evolution can explain why fish exhibit aggression because it is a primordial emotion. This emotion increases an individual’s survival or reproduction. Aggressive behavior can derive in fish species due to territory, sex specific selection and genetic variation. There is no specific fish species who display invasive behavior. Almost all the fish are aggressive sometimes in their lives depending on their surroundings. Fish territory, or in another word, defended areas are generally ruled by a single individual or by breeding pairs. The guarded resource may include food, shelter, sexual partner or offspring. While protecting their territory, fish often display aggressive behavior against their intruders. The territory owner strikes at competing fish directly ending in a bite, or a bump. Such aggressive behavior is seen in large juveniles, females and other fish of the same kind from the same territory. In order to better understand this topic, male threespine stickleback, Gasterosteus aculeatus, can be considered a good example (Bakker 1994). Theo Bakker his paper quoted the threespine stickleback male fish to be strictly polygynous, which means they prefer having two or more female mates in a territory. Thus a high level of aggressiveness occurs among the males in order to have access to females in a particular territory, which also gives rise to intrasexual selection among the male fish. Intrasexual selection is selection within the same sex. For instance, some male animals compete against one another, physically, for access to females for their kind. So, characters like big tail, sharp teeth or similar weaponry that can be used against other males of the same species as means of mating with females is a selective advantage. There is a deep relationship between the aggression in fish and the size of the territories owned by them. In a smaller territory, female fish often disappear before mating (Bakker 1994). Female fish are not bound to mate with a particular fish. If by chance a female get attracted to another male, she can dump the previous partner without any hesitation. In this situation, the ditched male fish become more aggressive to find their mates in order to reproduce. Their levels of aggression increase more when the rates of sneaking by rival males go up too. The sneaking males enter the nest and release their own sperm over the eggs of the breeding fish. The rival fish here are using alternative reproduction methods like parental, sneaker or satellite to avoid being hurt by breeding males. On the other hand, the breeding males have higher mating success and endure less looting of the eggs in large territories. Once the eggs have been gathered, the breeding males decrease their territories to protect their offspring from the predators during their parental phase. After the eggs have hatched, the males’ continue to show similar or more invasive behavior due to increased reproductive value of offspring and the awareness of newly hatched young fish against enemies (Bakker 1994). Territorial aggression can take place not only due to the pressure of mating, producing offspring, or intruders, but also from light intensity. The term intensity is used to describe the rate at which light spreads over a surface of a given area some distance from a source. At lower light levels, the risk of losing resources like food and mates give rise to aggressive behavior among the fish belonging to a territory (Sveinn K. Valdimarsson 2001). Additionally, for further understanding on how the rate of aggression and distance among neighboring fish varied with nighttime light intensities in the same area, Sveinn Valdimarsson and Neil Metcalfe conducted an experiment with the juveniles of Atlantic salmon, Salmo salar. At the beginning, S. salar were disclosed to four different nighttime light intensities (0.00, 0.01, 0.50 and 1.00 lx) for 24 hours period. From the result, it was concluded that fish showed less aggression when the intensity of the light was lower. This is because when the level of light was intense, due to darkness of night the territorial fish failed to detect their food or other members in the same area. So they decreased their territory size and remained closer to each other than attacking. This was a good example of evolution of cooperation among the fish. Additionally, as the light intensities of the light increased, those fish could see each other to defend their space. The territory size increases during bright lights. In short, the aggressive behavior of the salmon toward their rivals is highly manipulated by light intensities. Thus, the size of the space that the fish is defending increases or decreases between day and night. Male and female fish both get involved in aggressive confrontation. Yet varying selection pressures affecting each sex result in gender differences in aggressive syndrome during competition (Gareth Arnott 2009). Aggressive syndrome is a social condition describing an individual’s need to show his distaste or dislike against certain individuals. Adult female fish usually gather in groups, including adult females and non-reproductive males. Aggressive behavior is displayed in females especially when the female fish attack directly on each other. Dominance relationships can take place among female association. For instance, females of higher status (size) have better opportunities to mate than minors residing in the same group. Then females become aggressive when there are two dominant females trying to select the same male fish for mating. This selection can be based on intersexual selection, which is selection between two sexes. Females use such selection while choosing mates with good genes. For example, female peacocks tend to prefer male peacocks with bright plumage. The females think that if they mate with males having genes of bright plumage, the offspring will too have similar characteristic. S. Josefin Dahlbom, in his paper mentioned about an experiment done on zebra fish, Danio rerio to see the difference in aggression level between male and female if they are put together under similar situation (S. Josefin Dahlbom 2011). For this testing, a pair of males and a pair of females were sheltered together. As the experiment continued, it was observed that both dominant males and females increase their aggression level until day four. They measured this by observing how the males reacted with the females, or how the males behaved among themselves or how the females reacted with the other females. On the fifth day, the minor female members in the group learned to accept their lower rank and stopped challenging the dominant females. On the contrary, male subordinates remained fighting against the dominant males. As a result, the dominant males showed more aggression to suppress the minor males and to maintain their position among others. In the paper ‘Gender differences in aggressive behavior in convict cichlids’ Gareth Arnott and Robert W. Elwood investigated if gender related variations in aggression are seen in convict cichlids, Amatitlania nigrofasciata (Gareth Arnott 2009). In order to see gender-related changes in aggression, they tested if intersexual agonistic events take place between isolated males and females, who were not previously paired to each other as breeding partners. At the end, it was detected that in terms of encroachment, Texas cichlids males used lateral display along with tail biting; whereas, the females used frontal display with biting. There is an interesting explanation for these two different displays. Convict cichlids generally use either their left or right eye while swimming. Therefore, these fish use either their left or right hemisphere of the brain. Aggressive males are believed to use only their left hemisphere; whereas, aggressive females navigate based on their right eyes. Although a clear conclusion cannot be drawn from this study between the hemispheres and the aggression levels, it is fairly seen that males and females show variation in aggression syndrome. In short, various forces affecting each sex can result in distant aggressive behavior among male and female fish. Evolution of aggression can occur in fish due to their genetic makeup. In order to conclude a clear relationship between aggression and genetic makeup, a team from CNRS/Laboratoire Neurobiologie et Développement conducted an experiment on zebra fish, spiegeldanio (W. H. J. Norton 2011). At the beginning, the team of CNRS organized behavioral tests to quantitatively measure the three characters of aggressive behavior. In the experiment, it turned out that this particular fish has a mutation in its fgfr-1 gene summarizing for a membrane receptor sensitive to FGF, which is a key for growth factor in those fish. As a reaction to the mutation, this group of fish displays low brain levels of histamine. Histamine is a neurotransmitter that controls appetite, sleep and attention in a species. Due to low histamine levels, zebra fish exhibit aggressive behavior. Therefore, the link between the fgfr-1 genes to histamine regulates the behavioral status of aggression in zebra fish. In another experiment Katrina Tiira performed a different test on land-locked salmon, Salmo salar to see if juveniles with low estimated genetic diversity showed less aggression. In order to continue the theory, one group of fish with low genetic diversity and another group having high genetic diversity were selected. Then the aggressive levels were compared between these two groups. As a result, it was seen that salmon fry with low genetic variation showed less aggression than the other group. In the group of less variation, the researcher used closely related parents. The juveniles were genetically related sharing high number of alleles with each other. Thus, they display low aggression to their competitors as they used kin recognition method on others. In conclusion, it can be explained that genetic variation in salmon can manipulate the agnostic syndrome if the individuals in a group are closely related. Another interesting fact about aggression in fish is that it can increase by the effect of growth hormone, or GH, which has an essential growth factor in this species. They control the use of nutrients in tissue synthesis. Thus, it increases the metabolic demands in species resulting in aggression to fight for daily needs. For a better understanding an interesting experiment was designed on juvenile rainbow trout, Oncorhynchus mykiss (Elizabeth Jönsson 1998). They selected two control fish (C/C pairs), two growth hormone treated fish (GH/GH pairs) or one growth hormone-treated and one control (C/GH pairs). From the testing, it was analyzed that the GH increases aggression levels in all groups of O. mykiss. It indirectly improved the swimming activity along with the attacking rate between competitors. In summary, growth hormone plays a vital role in controlling aggression in rainbow trout and other fish. It is hard to name a specific group of fish with aggressive behavior as almost all of them show invasive actions towards each other. In order to compress the research, few examples of fish have been mentioned in this paper earlier to focus important areas, which include territory, gender specific selection and genetic divergence. These three conditions encourage fish to harm each other or display aggression.

Journal title needs added to refs. See format for refs for the journal "Evolution" to reformat these.

Annotated Bibliography for my references on "Reasons behind fish aggression" 1) Johnsson, Elisabeth, Johnsson, Jorgen, and Björnnsson, Thrandur. “Growth Hormone Increases Aggressive Behavior In Juvenile Rainbow Trout.” Pub Med.1998. 33(1):9-15. Print. The paper above was about the effects of growth hormone on the patterns of aggression in paired rainbow trout in juvenile condition. Later in the experiment, it was concluded that growth hormone levels indirectly increases the aggressiveness in fish. 2) Johnsson, JoÈrgen, Sernland, Emma, and Blixt, Marco.“Sex Specific aggression and anti-predator behavior in young brown trout.” Department of Zoology, Göteborg University, Göteborg, Sweden. Ethology, 2001: 107, 587-599. Print. This paper discussed the difference in the parental roles of male and the female fish with respect to aggressiveness of the males towards immature females. Here the researchers talked about maturation to an addition in the dominance and aggressive behavior in case of juvenile males of brown trout along with anti-predator behavior. Thus, the experiment in this paper helped to understand that immature males had higher aggressive behavior than females in case of intersexual contests, which might be associated with size differences. 3) Reebs, Stéphan. “Aggression in fishes.” Université de Moncton, Canada, 2008. Print. The research paper names ‘Aggression in fishes’ was about the competition among fish. Naturally, these species want to protect their genes or traits so they could continue to allow these genes to be expressed in the habitat. At the beginning of this paper, the writer mentioned two categories of competition, which counted exploitative and defense or interference competition. The first category referred to the first animals to get the food, habitat or mate would have advantages. On the other hand, the second one involved fighting and generally competing for mates, resources and habitats. Originally, this paper focused on how aggression could play vital role in various situation of interference competition including dominance hierarchies, territoriality and fighting of fish among themselves. In short, this paper would help to explain some basic ideas about how aggression can influence fish behavior most of the time. 4) Ruzzante, Daniel. “Domestication effects on aggressive and schooling behavior in fish.” Aquaculture. 1994. Volume 120, Issues 1-2. Print. This paper focused on the behavioral changes occurring during domestication since inbreeding wild and the domesticated species could have negative interaction. The schooling and agonistic behaviors were mainly observed for the experimentation also with the degree of aggressiveness. Thus, this paper would help to elaborate another different topic of how aggression is a part of fish life. 5) Vøllestad, Leif, and Quinn, Thomas. “Trade-off between growth rate and aggression in juvenile coho Salmon, Oncorhynchus kisutch.” Animal Behavior. 2003. Volume 66. Print. Aggressive behavior has been found to have evolutionary and developmental benefits like lowering of predator threats, attain dominance, territoriality and its defense with access to higher nutritive resources. Additionally, this paper mentioned that, the evolutionary behavior pattern was bound to have cost or tradeoffs like higher metabolic rate that had a hindering influence in the growth rate. The experiment in the paper was helpful to learn that heritability or genetic property of aggression was positive but with a value close to zero but the growth rate was high on the other hand.

https://en.wikipedia.org/wiki/Aggressionism Three Ways to improve the article 1. The article can use some definition on aggression as there is no particular definition for the word ‘aggressionism’. At first, a basic knowledge can be added on aggression and then the word aggressionism can be related to the details. In short, along with definition some examples can be shown to give the audience a better understanding of what aggression or aggressionism is really about. 2. Moreover, the article just introduces a single sentence about human aggression and how it leads to war but aggression is also seen in other animals like fish, monkeys and plants. Few sentences about various groups of animals will give a better view of aggression. 3. My topic on aggression mainly focuses on fish species and how this attitude can manipulate different aspects of their life. Moreover, it can also be added if there is any way the aggression in fish can be decreased or treated. It would be interesting to know that aggression can be noticed in fish due to dominance hierarchies, territoriality, sex, domestication and others. Citation:Reebs, S. 2008. Aggression in fishes. Howfishbehave.com: p.1-9