Wow! Sounds like your husband hasn't yet learned how to pick his battles. Why does he think it's important to convince his daughter that she hasn't tasted salmon? What is the issue? I venture to guess it's not salmon or what she's saying. I suggest he has a need to be in control and maybe can't tolerate anyone disagreeing with him. Or perhaps it's a form of needing to follow the rules, which your daughter also feels. That is a part of feeling in control. The rules say we don't lie, we don't make stuff up, we are to be 100% accurate, etc. And we must teach our children these things.
My daughter has gotten upset with her daughter lying from the time she was in preschool. The issue of telling the truth got lost in the emotional exchange that happened every time her daughter said anything that wasn't true, even when it was just fantasy at work. I suggest it might help your husband if he knew that his emotional insistence that your daughter be concretely truthful will only make it harder for her to be honest.
I suggest that she isn't lying. In her mind the water tastes like salmon. It doesn't matter if she's tasted salmon. Maybe she's smelled it. Taste and smell are closely related. Maybe someone talked about salmon and now she relates that conversation with the kitchen water. It really is no big deal. Why does your husband think it's worth fighting over?
In the scheme of life what difference does it make if she thinks the water in the kitchen tastes like salmon? He caused her to perhaps lie in his mind by insisting she hadn't tasted salmon. If he'd just let that go none of this would've happened. Can he see that? He set her up.
Is he a black and white thinker. Many people do not see the nuances in situations. Something either is or is not in their mind. Sounds like both of them were thinking that way. At 8, this is usual. An adult usually has come to realize that life is much more gray than black or white. Perhaps your husband hasn't realized that, yet.
And, how can he be 100% sure she's never tasted salmon? Is he with her 24/7? She's 8. Has she never been away from him? Can he be 100% sure she's not had salmon at Grandpa's, perhaps from a neighbor or friend?
Which leads me to one of my favorite sayings that helps me pick my battles. Would he rather be right or happy? Can he think about that and perhaps see that fighting over the taste of water and salmon just doesn't give him the happiness that he would like to have.
How does he feel about these bouts with his daughter? Would he like to get along better with her?
Is he confident that he's a good Dad or are these arguments a way for him to feel more confident? I suggest that when we know we're doing a good job we have less need to always be right.
There are usually beliefs unknown to us that cause us to react irrationally. I suggest that this is happening for your husband. I would urge him to find a different way of thinking about situations. Counseling helped me to find the gray in life.
I also agree that he's parenting in a similar way to his father. Is he willing to consider that possibility? Did he like the way his father was? If not, perhaps he would consider trying a different way. Perhaps a parenting class would help.
I've discovered over the years that the way I think influences the way I act and talk. I worked hard for many years to get rid of the words should and must. For him, what are those connected to? "She should always tell the truth. She shouldn't have any ideas that can't be proven." i.e. the fantasy that kitchen water tastes like salmon. Perhaps having a quiet conversation during calm times might help him understand.
BTW I lived in an apartment and could not stand the taste of the bathroom water. It didn't bother anyone else. There was no logical explanation for my distaste. The solution. I didn't drink out of the bathroom sink. Easy! No need to understand anything. Just do what works. Perhaps your husband could understand that concept. For him, yes, it makes no sense and it's OK if his daughter thinks differently.
I just noticed the comment, "she always gets what she wants." This tells me that it's quite possible that he's jealous of her. Otherwise why would it matter if she gets what she wants? Both of them can get what they want. It's not a competition.
I suggest that there are several things going on beneath the surface for your husband. I don't know of any way that you can change his reaction until he's able to recognize and accept how he feels. Once he does that he will be able to change what he says and does.