Propagation plays a vital role in freshwater mussel conservation, providing a way to restore declining populations, support recovery efforts, and advance the science needed to protect these remarkable species.
The life cycle of a freshwater mussel using in vivo (fish) and in vitro (lab) methods.
In Vivo Propagation
In vivo propagation follows the freshwater mussel’s natural reproductive process, allowing larvae to develop on host fish before growing into juvenile mussels.
Broodstock Collection
Most propagation involves collecting gravid females (females holding larvae) from the wild. With some species that are especially rare, the only way to obtain larvae is to gradually collect males and females over time so that they spawn in captivity.
Host Fish Collection
Host fish are sometimes collected from the wild by seining local streams. Some host fish species can be purchased from hatcheries. The Edenton National Fish Hatchery has propagated both Tessellated Darters and White Shiners for us to use in propagation.
Larval Collection
While some mussels species do best when allowed to release their larvae on their own, other species require that we flush the larvae from their gills using a water-filled syringe.
Glochidia (larvae) are placed in a small volume of water and bubbled together with the host fish for anywhere from 10-30 minutes on average.
Waiting for metamorphosis
Inoculated fish are held in recirculating aquaculture systems for 2-4 weeks depending on species and temperature until the metamorphosed juvenile mussels drop off. Those new mussels are swept into a mesh basket that is checked daily. Those new mussels are counted and moved into our rearing systems.
Juvenile mussels
When mussels first drop off the fish they are usually between 150-300 microns in size. That is barely visible to the naked eye as the tiniest of specks. This is microscope footage to show how active they are at this stage, constantly using their foot and the cilia on their foot and inside their shell to capture food particles and move them to their mouth.
In vitro culture uses modified cell culture techniques to rear freshwater mussels without a host fish. Here are some key points:
01
Host Fish Not Required
In vitro methods allow propagation to occur when host fish are unavailable or unknown.
02
Sterile by Design
Laval mussels are cultured under carefully controlled sterile conditions to promote healthy development and reduce contamination in their flasks.
03
Working Together
When used alongside in vivo propagation, in vitro methods increase augmentation numbers, improve methodological flexibility, and support research endeavors.
Ramshorn snails are hermaphrodites, meaning they possess both male and female reproductive organs. Snails held in captivity reproduce in specialized recirculating aquaculture systems.
Reproduction
In the wild, the Magnificent Ramshorn will lay eggs on the underside of vegetation like spatterdock. In the lab, we use artificial lily pads to simulate their natural environment.
Stocking
After the snails hatch, they are grown at our lab until they are the perfect size to be released back into the wild by the Nc Wildlife Resources Commission.
Many native North Carolina freshwater fish species face environmental challenges to their continued survival. One of the ways in which conservationists can help a species persist in their native habitat is to breed and rear individuals in captivity with the end goal of releasing these captive-bred animals back into their wild range. This process is called population augmentation.
Purpose
The goal of fish propagation programs at YMACC is to research optimal propagation methods while providing a consistent source of captive-bred fish for release programs designed and administered by the NCWRC.
Collection
Healthy wild parent fish, known as broodstock, are collected from their native streams in spring. They are brought into the lab and held together in groups for conditioning.
Conditioning
Broodstock are held in recirculating laboratory systems and allowed to acclimate to lab water quality, temperature, and lighting cycles. Their water temperature is slowly raised as nutrient-dense live feed is added to their diet to simulate breeding conditions in the wild.
Spawning
Grouped fish begin to pair off naturally during conditioning. When lab staff notices a pair of fish that have associated and begun to cohabitate under a saucer, they are moved to their own “honeymoon tank,” and given habitat under which to nest. Nests are monitored closely to determine health and proximity to hatching.
Hatching
Once the eggs inside the nest develop eyes, they are ready to be removed from the care of the male and added to a hatching basket in a different system. The eggs hatch and the baby fish drop through the bottom of the basket into their nursery tank.
Rearing
As the juvenile fish get older, they are split into tanks of different volumes and densities of fish. They eat voraciously and can exclude each other from feeding, so lab staff monitor their growth and behavior closely.
Release
When the fish reach between 80 mm and 100 mm in length, they are deemed ready for release. NCWRC staff choose stocking locations and tagging methods for the propagated fish before taking them into the wild in the fall and late spring.
