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STOCKTON FWO: Trans-Generational Marking Reveals the Origin of Juvenile Delta Smelt
California-Nevada Offices , October 9, 2009
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Trans-generational marking of adult Delta Smelt at the UC Davis Fish Conservation and Culture Laboratory.  Shown is micro syringe used to inject strontium chloride hexahydrate (Photo by Dr. James Hobbs, UC Davis).
Trans-generational marking of adult Delta Smelt at the UC Davis Fish Conservation and Culture Laboratory. Shown is micro syringe used to inject strontium chloride hexahydrate (Photo by Dr. James Hobbs, UC Davis). - Photo Credit: n/a
A: Sagittal otolith of juvenile delta smelt showing daily growth increments and B: same otolith highlighting the primordia (core region of otolith) where Strontium concentration and 87Sr: 86Sr were measured at the Interdisciplinary Center for ICP-MS, UC Davis (photo by Dr. James Hobbs, UC Davis).
A: Sagittal otolith of juvenile delta smelt showing daily growth increments and B: same otolith highlighting the primordia (core region of otolith) where Strontium concentration and 87Sr: 86Sr were measured at the Interdisciplinary Center for ICP-MS, UC Davis (photo by Dr. James Hobbs, UC Davis). - Photo Credit: n/a

by Gonzalo Castillo, Stockton FWO
Trans-generational marks transferred from female fish to their offspring can be both natural, reflecting the environment the mother has lived in, or artificial, by exposing adult females to enriched stable isotopes or elements.

The U.S. Fish and Wildlife Service, in coordination and collaboration with Dr. James Hobbs, Interdisciplinary Center for Mass Spectrometry (ICP-MS) and Dr. Joan Lindberg, Fish Culture and Conservation Laboratory (FCCL), both of the University of California Davis (UC Davis), recently conducted the first artificially induced trans-generational marking experiment on delta smelt.

The project, funded by the U.S. Bureau of Reclamation, provided a means to distinguish between wild juvenile delta smelt entrained in the State Water Project (SWP), South Delta, CA, and those juvenile delta smelt potentially produced by cultured adult smelt released into Clifton Court Forebay (CCF).  Due to increased concerns regarding the take of delta smelt at the Skinner Fish Facility, SWP, this additional mark was requested by the Department of Water Resources (DWR) as part of a provision to implement the final phase of a three-year mark-recapture study in the Forebay funded by the CALFED Science Program and the Interagency Ecological Program.

An effective and timely method was required to distinguish between wild-origin, and cultured-origin, juvenile delta smelt salvaged from the Skinner Fish Facility over the 2009 spring salvage season. As part of this project, an otolith trans-generational marking experiment was conducted by producing an artificial tag that would be passed from the mother to egg and incorporated into the otolith primordia of the progeny, where it would make a chemical fingerprint identifiable through laser ablation at an older age.  As part of the test to determine the feasibility of this method, adult females were injected abdominally with strontium chloride hexahydrate (hereafter Sr; 30 mg/L Sr, 15 mg Sr/L, or saline vehicle), spawned manually, and offspring were reared at the FCCL for 60 days before evaluating otoliths for trans-generational mark through laser ablation ICP-MS.   Results showed strontium concentration was significantly elevated in the otolith primordial for progeny of fish injected with 30 mg Sr/L relative to either fish injected with 15 mg/L Sr, or controls.

Prior to mark-recapture releases, all adult fish destined for release in CCF were injected with 30 mg Sr/L, both male and female fish were marked due to the lack of distinguishing characteristics between the sexes.  Juvenile delta smelt (at least 20mm fork length) collected in salvage operations from the Skinner Fish Facility were transported on a daily basis to the UC Davis Interdisciplinary Center for Mass Spectrometry and examined for the unique Sr mark recorded in the otolith. Results from 157 juvenile delta smelt collected from May to July 2009, revealed that none of these juveniles were derived from marked fish.  Thus, corroborating the extremely unlikely probability that cultured adult delta smelt would survive and subsequently reproduce in the Forebay,  as inferred from previous pre-screen loss experiments and quantitative modeling.   

Another important contribution of this study, to be completed in the year 2010, will be a better understanding of the natal origin of wild juvenile delta smelt entrained by the State Water Project in the South Delta.

 


Contact Info: Gonzalo Castillo, 209-334-2968x323, gonzalo_castillo@fws.gov



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