A man accused of murdering his ex-girlfriend's baby has claimed the child's mother played a game in which she shook the six-week-old.
Mark Simpson, 29, said he treated six-week-old Alexis Matheson as his own child and would not have harmed her.
He said nearly every day Illona Sheach shook the baby without supporting her head as part of a game called 'fishy'.
Mr Simpson denies murdering Alexis by assaulting her in Aberdeen between 8 November and 9 December 2007.
He cried as he told the High Court in Aberdeen of the moment he found the young baby lifeless in her bouncy chair in his home on 9 December, 2007.
Defence lawyer Herbert Kerrigan QC asked: "Did you see anything happening to Alexis that gave you cause for concern?"
Mr Simpson replied: "The only time it gave me cause for comment was when Illona would do this thing she called 'fishy'.
"Illona would be lying on the floor on her back with her knees up. She would hold Alexis by the ribs shaking Alexis back and fore but there was no support to the head."
Mr Kerrigan asked: "I take it it was regarded as some sort of game?"
He replied: "Yeah, I thought it was a game. I thought it was something you shouldn't do to a child of this age."
Mr Kerrigan asked: "How often would she do this to the child?"
Mr Simpson replied: "It was often a daily occurrence."
He told the court he could previously think of no reason for the child to have suffered broken ribs or injuries consistent with shaking, and said it was only when he heard evidence given by medical experts last week that he remembered his concerns over the game.
Earlier he told the jury how he discovered the baby floppy and lifeless on the night she was rushed to hospital.
He said he had noticed Alexis began to become unwell when she started projectile vomiting five days before her death, after being fed.
The court heard the young baby sneezed violently and the couple spotted specks of blood on her nose.
He told the court: "I went through and found that she was very floppy, very lifeless. The light was quite dark. I took her through to the kitchen then I realised that her lips were blue.
"I took her her back through to the sitting room. I started unbuttoning her babygrow and made a comment about Illona phoning an ambulance.
"By that point Illona was in hysterics. I wasn't exactly coping well myself, I just had to deal with the situation."
Mr Simpson said he checked for a pulse which was faint and then disappeared completely, then gave the baby CPR.
He added: "So I had no choice but to do CPR. I remember passing comment to Illona maybe about damaging a rib or something but my head was in a panic."
He described to the court how he heard a noise from the baby after doing compressions and said his mum arrived and he continued giving the baby CPR on the way to Aberdeen Royal Infirmary.
Asked why he did not dial 999 straight away, he replied: "I should have but I panicked. It's not every day you see a child at that age blue on your living room floor."
Earlier the court heard how Mr Simpson was "annoyed" about being left alone with the child for four hours because he felt Ms Sheach was "dodging" bathing duties.
The trial continues.