Iomega Corp. has declared first-quarter net income of $2.7 million or 16 cents per share, up from $2.5 million or 15 cents per share in the same period last year.

The earnings increase came on sales of $31.5 million up from $29.1 million in the first three months of 1990.Pretax earnings increased by 38 percent to $3.8 million in the first quarter of 1991, up from $2.8 million in the same period last year. Io-mega said the gains came from increased sales, higher gross margins due to improved manufacturing performance, and product cost reductions.

Partially offsetting these increases were additional expenses incurred in research & development for investments in various products, plus a higher effective tax rate.

Income taxes were provided at a 30 percent rate in the first quarter of 1991, compared to a 10 percent rate in the first quarter of 1990. The tax rate increased because prior year loss carryforwards are no longer available to offset the tax provision.

The company said its balance sheet remains strong. Cash and temporary investments at March 31 were $28.3 million, compared to $29.1 million on Dec. 31. The decline in cash resulted from a decrease in accrued liabilities, an increase in accounts receivable, and the purchase of capital equipment.