HISTOPATHOLOGY, BLOOD-CHEMISTRY, AND PHYSIOLOGICAL STATUS OF NORMAL AND MORIBUND STRIPED BASS (MORONE-SAXATILIS) INVOLVED IN SUMMER MORTALITY (DIE-OFF) IN THE SACRAMENTO-SAN-JOAQUIN DELTA OF CALIFORNIA

Summer mortality ('die-off') is common in striped bass, Morone saxatil is (Walbaum), in the San Francisco Bay-Delta region. Tissue and blood samples of moribund and healthy striped bass collected during the summ ers of 1986-1988 were analysed. Sixteen moribund and 25 healthy refere nce fish from the Carquinez Strait area and eight fish caught in the P acific Ocean were studied. Moribund fish plasma was invariably yellow- orange; most of the moribund fish had discoloured livers with haemorrh agic regions, and approximately one-third had haemorrhagic intestines. Plasma levels of aspartate aminotransferase, uric acid, alkaline phos phatase and cortisol were significantly higher than in reference fish from Carquinez Strait and the Pacific Ocean, whereas cholesterol, sodi um, chloride, triiodothyronine and glucose levels were significantly l ower. Hepatic heavy metal concentrations and bacterial content were si milar in moribund and reference fish. Gill Na+,K+-ATPase activity was significantly lower in moribund fish. Liver, kidney, intestine, and th yroid follicles of moribund fish displayed various histopathological c hanges, and corticosteroidogenic (interrenal) tissue could not be iden tified positively in moribund fish. These findings are discussed in re lation to recent work on the chemical burdens (industrial and agricult ural hydrocarbons) found in livers from some of the fish examined in t his study.