The Insulin-Like Growth Factor-1 (IGF1) System as a Potential Biomarker for Nutritional Status and Growth Rate in Pacific Rockfish (SEBASTES SPP.)

Growth performance in vertebrates is regulated by environmental factors including the quality and quantity of food, which influences growth via endocrine pathways such as the growth hormone (GH) / insulin-like growth factor somatotropic axis. In several teleost fishes, circulating concentrations of insulin-like growth factor-1 (Igf1) correlate positively with growth rate, and it has been proposed that plasma Igf1 levels may serve as an indicator of growth variation for fisheries and aquaculture applications. Here, I tested whether plasma Igf1 concentrations might serve as an indicator of somatic growth in olive rockfish (Sebastes serranoides), one species among dozens of rockfishes important to commercial and recreational fisheries in the Northern Pacific Ocean. I reared juvenile olive rockfish under food ration treatments of 1% or 4% wet mass per d for 98 d to experimentally generate variation in growth. Juvenile rockfish in the 4% ration grew 60% more quickly in mass and 22% faster in length than fish in 1% ration. Plasma Igf1 levels were elevated in rockfish under the 4% ration, and individual Igf1 levels correlated positively with growth rate, as well as with individual variation in hepatic igf1 mRNA levels. These data in olive rockfish support the possible use of plasma Igf1 as a positive indicator of growth rate variation in rockfishes. Using my findings from this experiment, I further investigated the use of this biomarker in wild rockfish by examining patterns of Igf1 variation in blue rockfish (Sebastes mystinus) caught within and outside of two Marine Protected Areas (MPAs) along California’s coast: Piedras Blancas MPA and Point Buchon MPA. Individual Igf1 levels correlated positively with increasing size as seen in laboratory reared fish. After correcting plasma Igf1 values for body size, circulating Igf1 was observed to be higher in blue rockfish within the boundaries of the Piedras Blancas MPA compared to fish from an adjacent site with no fishing restrictions. Igf1 levels in blue rockfish caught within the Point Buchon MPA, however, were similar to those outside of that MPA. These results suggest that blue rockfish within the Piedras Blancas MPA may experience enhanced growth relative to conspecifics outside of that MPA’s boundaries, and that such growth increases may be specific to MPA locations. My findings support previous studies that Igf1 is a positive indicator for growth in teleost fish and can be used as a tractable biomarker in wild rockfish which could enhance management efforts of fish stocks within marine protected areas