Oliver Fish, known mostly by his last name, joined the Llanview Police Department in early 2008 when Llanview Police Officer Talia Sahid was transferred to the nearby Cherryvale Police Department. Sweet but awkward, Fish's stellar computer skills proved helpful to Detective John McBain on numerous occasions. Fish was transferred back to Cherryvale when Talia got her old job back, but John called him back into service to help him unwrap the mystery surrounding a woman staying in Todd Manning's apartment. Fish tapped into his computer skills to track down Todd's former bodyguard, who identified the mystery woman as believed-dead Marty Saybrooke.

Fish developed a crush on Layla Williamson, but Layla wouldn't pay him the time of day. During the Go Red Ball in February, Fish encountered a blonde beauty named Stacy Morasco, who invited him back to her place for sex. The next day, simpleminded Fish assumed that he and Stacy were now an item and promptly went to Layla and told her he was unavailable. When Fish returned to Stacy, she laughed in his face and said their encounter was nothing more than a one-night stand.

As Fish was helping John McBain investigate a series of murders in Llanview, clues began pointing to the 1993 rape of Marty Saybrooke at the KAD fraternity house at Llanview University. Fish told John that he was once a member of the fraternity. Fish was shocked to run into a fellow fraternity member, Kyle Lewis, who was working as a lab technician at Llanview Hospital. Fish and Kyle shared an awkward exchange, since they had fallen out of contact since attending school together.

In June, Oliver answered an ad for a roommate, not realizing that it was the apartment shared by Layla and Cristian. Layla initially was reluctant to let Fish move in, but after he proved himself capable of hooking up their TV with a new converter box, she relented.

After running into Kyle in the park, Fish quickly asked Layla to go out on a date with him, and despite her reservations she agreed. Cristian warned Fish not to hurt Layla, saying he was concerned for his friend. While on a date at the Palace Hotel, Layla noticed the male waiter checking out Oliver and pointed it out to Fish, who seemed to get flustered. Layla explained that it didn't mean Oliver was gay, and just then Oliver said he wanted to continue the date back at the apartment. Their evening was interrupted by Cristian, however, who told Fish that Kyle had told him that Oliver wasn't who he seemed to be. Fish said Kyle was just jealous because he wanted Layla for himself.

Based on Fish's advice, Layla got a job at the Llanview Police Department as Detective John McBain's assistant. She told Fish she didn't want anyone at work to know they were dating and got angry when Fish quickly spread the word. Fish explained that he was just proud of Layla and wanted to fit in with the rest of the guys. But when Layla tried to get intimate, Fish backed off, prompting Layla to ask Fish if he was gay. Fish denied it, noting he had slept with Stacy, and accused Layla of not taking their relationship seriously. Layla apologized, but then Cristian arrived home and told Layla that something had gone down between Kyle and Fish while they were in college. Layla told Cristian to mind his business, and she and Fish tried to get back on track.

In August, after learning that Kyle had told Roxy Balsom that he and Oliver were involved in college, Oliver confronted Kyle and the two got into a heated exchange in the ally behind the Buenos Dias Café. Kyle accused Oliver of being scared to accept that he was gay and told Oliver that he still loved him. Oliver tried to deny being gay, but Kyle pressed him to admit that they meant something to each other, and the two ended up in a passionate kiss. Cristian oversaw the kiss and confronted Fish, who claimed that Kyle had been stalking him. Cristian could tell Fish was lying and told him to come clean to Layla, or he would be forced to. Fish made several attempts to tell Layla the truth but chickened out. After putting Layla on the phone with his parents, who were excited to talk to the girl dating their son, Fish and Layla headed to her bedroom and had sex for the first time. After learning that Fish and Layla had sex, Cristian lashed out at Fish for not telling Layla the truth, but Fish denied being gay, saying he had only experimented with Kyle in college.

Fish was stunned to arrive home one night to a bitter Layla, who had learned about Fish's relationship with Kyle and demanded that Oliver admit the truth. Under intense questioning, Fish admitted that he and Kyle were together in college but denied he was gay. When Layla brought up the recent kiss between Oliver and Kyle, Oliver claimed that Kyle had pushed himself on him. Layla refused to believe it and begged Oliver to admit to himself and to her that he is gay. But Fish refused, forcing Layla to order him out of the house. A shaken Fish ended up at Rodi's, where Kyle confronted him about denying that he was gay. Stacy overheard the entire conversation and cozied up to Fish, ordering him drinks until he was so drunk that he went back to her place and had sex with her. The next morning, Fish was horrified to realize what he had done. He went back to the apartment and admitted to Layla and Cristian that he was gay. Fish volunteered to move out, but Cristian and Layla sympathized with him and asked him to stay.

When Fish's conservative parents said they were coming to town, Layla encouraged Fish to come out to them. Cristian even bought him a "how to" book about coming out to your parents. As Fish prepared to tell his parents the truth, his father discovered the book by accident and assumed that Cristian was gay. He excoriated Cristian for leading a gay lifestyle and told Fish that he would need to move out of the apartment, which prompted Fish to reveal the truth to his parents. Fish's father could hardly believe it, but Fish said his mother knew it was true because she once walked in on Fish in bed with Kyle in college. Fish broke up with Kyle because he was so ashamed, and he and his mother never spoke of the incident again. Fish's mother said she thought it was just a phase, prompting Fish's father to storm off. While on a police assignment at the hospital, Fish ran into Kyle and told him that he had come out to his parents, although only after having drunken sex with a girl. Back at the apartment, Fish's mother arrived without her husband and told Fish that she believed he could change if he wanted to. But Oliver said it wasn't a choice and that he needed his mother to accept him for who he was. On their way out of town, Fish's dad told Fish that although he loved him, he couldn't accept his "lifestyle."

Fish hoped to resume a relationship with Kyle after coming out, but Kyle said it was too late and that he was already seeing another guy, Nick Chavez. Fish was stunned to walk into the Buenos Dias Diner in October 2009 to see Kyle accepting Nick's marriage proposal. Kyle told Fish he agreed to marry Nick as part of a mass commitment ceremony organized by Nick and out lesbian Amelia Bennett to raise awareness of the need for gay marriage rights. The day before the wedding, Fish told Kyle he loved him and said he wanted a chance to have a relationship with him, but Kyle said he was afraid a relationship with Oliver would mean a life of living in the closet. As the commitment ceremony was about to begin, Fish confronted a group of protesters and, on live television, admitted he was gay. Kyle decided right then and there that he couldn't go through with marrying Nick, and he and Oliver agreed to begin dating.

Oliver and Kyle slowly got to know each other once again and planned for their first date, which was interrupted when Oliver was called away on police business. When they prepared to make love for the first time since college, they were interrupted by news that Kyle's ex, Nick, had been beaten up by a group of gay-bashing thugs. Oliver was supportive of Kyle as he helped Nick recover, but became suspicious when Nick said he had no place to go and moved into Kyle's studio apartment. Oliver and Kyle got in an argument about Nick, and Kyle later learned that Nick was playing him and wanted to get back together. Kyle rejected Nick's advances and went after Oliver, finding him just before midnight on New Year's Eve. They rang in the start of 2010 by making love. Oliver was hired by Rex to look after Stacy and her unborn baby, who were being threatened by Rex's evil father Mitch Laurence. Oliver confided in Kyle that he and Stacy had made love, and Kyle told a stunned Oliver that he could be the father of Stacy's baby, since she had lost Rex's baby and gotten pregnant around the same time they had sex. Kyle and Oliver confronted Stacy and her pal Kim, but they denied that Oliver was the baby's father and stuck to the lie that Schuyler was the daddy. Though they threatened to tell Rex and Schuyler the truth, they backed down after Stacy and Kim said they would have Kyle thrown out of medical school for breaking doctor-patient confidentiality. Oliver wasn't sure what to believe, but Kyle said Stacy couldn't be trusted and could be blackmailing Schuyler. Oliver said they would have to wait until the baby was born to learn the truth, and he told Kyle and Stacy that he wasn't ready to be a father yet anyway.

After a pregnant Stacy was kidnapped by one of Mitch's goons, Oliver and Rex searched for her on Llantano Mountain and came across Schuyler Joplin, who confessed to Rex that he was the father of Stacy's baby. Stacy delivered a baby girl, named Sierra Rose, before falling into a sheet of ice and drowning. At the hospital, Sierra needed to have emergency heart surgery and Schuyler revealed to Gigi that he was Sierra's father. Kyle urged Oliver to have a DNA test to determine if he was actually the father, but Oliver refused. Kyle had the test done anyway and presented Oliver with the sealed envelope containing the results, but Oliver lashed out at Kyle for breaking the law and refused to open the letter. Allison Perkins later kidnapped the baby from Schuyler's home and tied up Roxy and Kyle before going to Statesville Prison to see Mitch. Fish freed them both and, after learning that Sierra had been kidnapped, opened the paternity test and learned he was Sierra's father. Fish told Schuyler the truth and was united with his daughter. He and Kyle brought the baby home and prepared to raise her. Fish stood up in court and affirmed he was Sierra's biological father, and the court awarded him full custody. Fish and Kyle told both Gigi and Roxy that they would always be a part of Sierra's life.