Methods for the Smelts

Aquaculture Method Development for Delta Smelt:

Through the integration of numerous experimental findings, the FCCL was able to increase survival rates to a level sufficient for the successful culturing of delta smelt from egg through adult stage; with the first complete life cycle in captivity being established in 2000-2001. Currently, the FCCL focuses on improving existing rearing techniques, with the goal of increasing the system’s efficacy and rearing success. Some of our current areas of emphasis are described below.

❖ Tank size and system parameters – As fish develop from newly hatched larvae to adults, they are transferred multiple times between fish-rearing systems to cater to the needs of each life stage. Black interior tanks are used for all fish, as clear and acrylic tanks have been found to stress fish. Light is administered to tanks, with varying intensities corresponding to what has been deemed optimal for each life stage. Each recirculating system provides UV sterilization, both particle and biological filtration, and heat pumps for temperature control. Currently the FCCL is testing stocking densities and feeding rates for each tank. We are also in the process of developing smaller culturing systems for research purposes.

❖ Turbidity Effect– Early-larval and late-larval stages require different turbid environments to promote feeding. While it is not completely understood why larval stages require turbidity, it is thought that the suspended particles provide a visual contrast that enables them to better find their prey. Turbidity is introduced via the addition of concentrated algae. As fish mature into the adult stage, algal addition is gradually decreased in order to gently transition the fish into clearer water environments.

❖ Weaning strategies – As the smelt develop, they are transitioned from a live prey diet to a dry feed diet. The FCCL is currently researching this topic, in attempt to determine the best time for weaning.

❖ Salinity – In their natural environment, delta smelt inhabit estuary areas of relatively low salinity. The precise environmental salinity values vary seasonally in accordance with each year’s freshwater availability. In collaboration with researchers at UC Davis, the FCCL is conducting experiments that analyze the physiological effects of salinity on delta smelt.

Related Publications:

Tsai YJJ, Ellison L, Stevenson T, Carson EW, Hung TC (2023) No effect of stocking density on the survival or size of late-stage delta smelt larvae reared in a small-scale culture system, North American Journal of Aquaculture 85(4), 395-400.

Tsai YJJ, Ellison L, Stevenson T, Mulvaney WJ, Carson EW, Hung TC (2022) Evaluating the performance of a small-scale culture system for delta smelt (Hypomesus transpacificus), North American Journal of Aquaculture 84(3), 370-380.

Hung TC, Ellison L, Stevenson T, Sandford M, Schultz AA, Eads AR (2022) Early weaning in endangered Delta Smelt: effect of weaning time on growth and survival, North American Journal of Aquaculture 84, 249-260.

Tigan G, Mulvaney W, Ellison L, Schultz A, Hung TC (2020) Effects of light and turbidity on feeding, growth, and survival of larval Delta Smelt (Hypomesus transpacificus, Actinopterygii, Osmeridae), Hydrobiologia 847(13), 2883-2894.

Lindberg JC, Tigan G, Ellison L, Rettinghouse T, Nagel MM, Fisch KM (2013) Aquaculture methods for a genetically managed population of endangered delta smelt, North American Journal of Aquaculture 75(2), 186-196.

Hung TC, Piedrahita RH (2011) The performance and impact of a bubble-wash bead filter in a recirculating green water larval culture system for delta smelt (Hypomesus transpacificus), Aquacultural Engineering 45, 60-65.

Baskerville-Bridges B, Lindberg J, Doroshov S (2004) The effect of light intensity, alga concentration and prey density on the feeding behavior of delta smelt larvae, in F. Feyrer, L. Brown, R. Brown, J. Orsi, editors. Early life history of Fishes in the San Francisco Estuary and Watershed. American Fisheries Society Symposium 39, 219-227.

Aquaculture Method Development for Longfin Smelt:

In 2008 the FCCL became involved in the process of developing fish culture methods for the longfin smelt, another listed smelt species native to the San Francisco Bay estuary. The FCCL has developed a culture method in attempt to produce a reliable culture of longfin smelt, although establishment of the first successful culture is still in the near future. Currently, the longest time that we have successfully held an F1 longfin smelt in lab is 327 days post hatching. The longest time that we have successfully held a wild caught longfin smelt in lab is 173 days.

In attempt to develop a methodology for culturing longfin smelt, we have used the same aquaculture systems previously designed for delta smelt. However, various manipulations have been made in salinity, feed, and tank size in order to increase the timespan of longfin smelt survival. During our first few years of culturing attempts, we faced two predominate obstacles; (1) wild-caught broodstock exhibited high occurrences of fin rot which resulted in high mortality, and (2) wild-caught broodstock refused to eat in culture. As a result, the FCCL could only hold wild-caught longfin smelt in culture for 2-3 weeks and try to spawn them before their death. However, experimental attempts in following years provided solutions to these problems. The improvements made have enabled us to house wild-caught longfin smelt on site for much longer periods of time, and, as a result, increase the number of pair-crosses we perform each year. In addition to finding new way to make our existing methods more practical and efficient, we are investigating techniques for increasing F1 longfin smelt survival in culture. We are currently collaborating with UC Davis research groups for the purpose of defining the niche of cultured longfin smelt from egg to larval stage, providing us with a greater insight on how to optimally rear early stages in culture.

Related Publications:

Hung TC, Rahman MM, Lewis LS, Yang YC, Stevenson TA, Menard KL, Connon RE, Bell H, Fangue NA (2023) Laboratory-bred Longfin Smelt produced offspring in the first year in captivity, North American Journal of Aquaculture.

Rahman MM, Lewis LS, Fangue NA, Connon RE, Hung TC (2023) Effects of salinity on fertilization, hatching, and larval performance of longfin smelt Spirinchus thaleichthys, Aquaculture Research 2023, 9984382.

Mulvaney W, Rahman MM, Lewis LS, Cheng J, Hung TC (2022) Captive rearing of longfin smelt Spirinchus Thaleichthys: First attempt of weaning cultured juveniles to dry feed, Animals 12, 1478.

Yanagitsuru YR, Main MA, Lewis LS, Hobbs JA, Hung TC, Connon RE, Fangue NA (2021) Effects of temperature on hatching and growth performance of embryos and yolk-sac larvae of a threatened estuarine fish: longfin smelt (Spirinchus thaleichthys), Aquaculture 537, 736502.

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