Stable Car bon Iso tope Ratios and Stan dard Pro duction Data as Indices of Golden Shiner, Notemigonus crysoleucas, Per for mance in Pond Feed ing Trials

Abstract

This study shows the ef fect of production variables on assimilation of foods by golden shin ers, Notemigonus crysoleucas, in ponds was ex am ined in con cur rent 8-week feed ing tri als at the Uni versity of Ar kan sas at Pine Bluff (UAPB) and Texas A&M Uni ver sity (TAMU). Ten 0.04-ha ponds per site were fer til ized with defatted rice bran and stocked with golden shin ers (ini tial weight = 1.3 g) at a rate of 750,000/ha (UAPB) or 375,000/ha (TAMU). Fish in five ponds per site were fed a nu tri tion ally com plete pre pared diet at 4% of body weight, while fish in the re main ing ponds were not fed. As sim i la tion of nat u ral foods by “unfed” fish was com pared to that of fish fed the pre pared diet at each site. Stan dard pro duc tion data (weight gain, Secchi depth, dissolved ox y gen [DO]) were com pared to sta ble car bon iso tope ra tio (d1 3 C) data as an in dex of fish per for mance (weight change or fish d13 C, re sult ing from as sim i la tion of var i ous food sources). Fish weight change and fish iso tope ra tio were re gressed sep a rately against in de pend ent vari ables (feed amount, Secchi depth, DO, fed/unfed dummy vari able, and study site dummy vari able) to de ter mine their re la tion ships. Nat u ral pro duc tiv ity was con sis tently lower at TAMU than at UAPB, while temper a ture and min i mum DO were sim i lar be tween sites. Weight gains of fed and unfed fish at TAMU were higher than those of fed and unfed fish at UAPB. The d13 C of fed and unfed fish at UAPB changed lit tle dur ing the study and did not al low dis crim i na tion among their food sources. The d13 C of fed fish at TAMU ap proached that of the pre pared diet, while that of unfed fish re sem bled that of the plank ton and rice bran. Pre pared diet quan tity and the study site sig nif i cantly (P > 0.1) af fected fish weight change, but Secchi depth and min i mum DO did not. Weight gain increased with in creas ing diet in put up to a max i mum value, then de clined with ad di tional in puts. Min i mum DO, plank ton iso tope ra tio, and the fed/unfed and site vari ables sig nif i cantly af fected fish iso tope ra tio.