、。
Rice shops are, as everyone knows, a declining industry.
Literal
Rice-shop [topic-は], needless-to-say well-known declining-industry.
言わずと知れた is a set participial phrase meaning 'known without saying / as everyone knows' — literally 'without saying, known.' 斜陽産業 'declining industry' (斜陽 'setting sun' + 産業 'industry') is a vivid compound. お米屋さん uses the polite お prefix + 屋 'shop' + さん for the neighborly, familiar register. A compact, punchy observation.