Balloon Tag Manufacturing Technique for Sensor Fish and Live Fish Recovery

Summary

A protocol is presented for designing and manufacturing balloon tags to recover Sensor Fish and live fish, allowing assessment of their physical condition and biological performance in hydraulic structures. The method optimizes balloon tag performance by considering factors such as balloon volume, inflation/deflation times, component selection, and the characteristics of the injected water.

Abstract

Fish may experience injuries and mortality when they pass through hydraulic conveyances at hydropower dams, even if these conveyances are designed to be fish-friendly, such as downstream bypass systems, modified spillways and turbines. The main methods used to study fish passage conditions in hydraulic structures involve direct, in situ testing using Sensor Fish technology and live fish. Sensor Fish data helps identify physical stressors and their locations in the fish passage environment, while live fish are assessed for injuries and mortality. Balloon tags, which are self-inflating balloons attached externally to Sensor Fish and live fish, aid in their recovery after passing through hydraulic structures.

This article focuses on the development of balloon tags with varying numbers of dissolvable, vegetable-based capsules containing a mixture of oxalic acid, sodium bicarbonate powders, and water at two different temperatures. Our research determined that balloon tags with three capsules, injected with 5 mL of water at 18.3 °C, consistently achieved the desired balloon volume. These tags had a mean inflation volume of 114 cm³ with a standard deviation of 1.2 cm³. Among the balloon tags injected with water at 18.3 °C, it was observed that the two-capsule balloon tags took the longest time to reach full inflation. In addition, the four-capsule balloon tags demonstrated a faster inflation start time, while the three-capsule balloon tags demonstrated a faster deflation start time. Overall, this approach proves to be effective for validating the performance of new technologies, improving turbine design, and making operational decisions to enhance fish passage conditions. It serves as a valuable tool for research and field evaluations, aiding in the refinement of both the design and operation of hydraulic structures.

Introduction

Hydropower is a significant renewable energy resource worldwide. In the United States, hydropower contributes an estimated 38% or 274 TWh of electricity generated from renewable sources¹ and has the potential to add approximately 460 TWh per year². However, as hydropower development increases, concerns about fish injury and mortality during hydraulic passage have become paramount³. Various mechanisms contribute to fish injuries during passage, including rapid decompression (barotrauma), shear stress, turbulence, strikes, cavitation, and grinding⁴. Although these injury mechanisms may not have an immediate impact on the overall condition of the fish, they can render them more vulnerable to diseases, fungal infections, parasites, and predation⁵. Additionally, direct physical injuries resulting from collisions with turbines or other hydraulic structures can lead to significant mortality, emphasizing the importance of mitigating these risks in hydropower development.

One of the most common methods for evaluating fish passage conditions is releasing Sensor Fish and live fish through hydraulic structures^6,7. The Sensor Fish is an autonomous device designed to study the physical conditions that fish experience during passage through hydraulic structures, including turbines, spillways, and dam bypass alternatives^8,9. Equipped with a 3D accelerometer, 3D gyroscope, temperature sensor, and pressure sensor⁹, the Sensor Fish provides valuable data on fish passage conditions.

Balloon tags, which are self-inflating balloons attached externally to Sensor Fish and live fish, assist in their recovery after passing through hydraulic structures. The balloon tags consist of dissolvable capsules filled with gas-generating chemicals (e.g., oxalic acid and sodium bicarbonate), a silicone stopper, and a fishing line. Prior to deployment, water is injected through the silicone stopper into the balloon. The water dissolves the vegetable-based capsules, triggering a chemical reaction that produces gas inflating the balloon. In this neutralization reaction, sodium bicarbonate, a weak base, and oxalic acid, a weak acid, react to form carbon dioxide, water, and sodium oxalate¹⁰. The chemical reaction is provided below:

2NaHCO₃+ H₂C2O₄ → 2CO₂ + 2H2O + Na₂C₂O₄

The inflated balloon increases the buoyancy of the Sensor Fish and live fish, enabling them to float on the water surface for easier recovery.

The number of balloon tags required to achieve flotation and facilitate the retrieval of a sample (e.g., Sensor Fish or live fish) may vary based on the volume and mass characteristics of the sample. The duration of balloon tag inflation can be adjusted by injecting water at different temperatures. Colder water will increase the inflation time, while warmer water will decrease it. Balloon tags have been successfully employed in various locations, including the Farmers Screen, a unique horizontal, flat-plate fish and debris screen structure in Hood River, Oregon¹¹, and a Francis turbine at Nam Ngum Dam in the Lao People's Democratic Republic¹². Another commercially available balloon tag example is the Hi-Z Turb'N Tag^13,14. The Hi-Z Turb'N Tag allows inflation time to be adjusted between 2 min and 60 min, depending on the injected water temperature¹³. This technology has been used in fish studies at many field sites, including studies involving Chinook salmon smolts released at Rocky Reach Dam on the Columbia River and juvenile American shad at Hadley Falls Dam on the Connecticut River^15,16. Both technologies utilize acid-base chemical reactions to inflate the balloon tags for recovery.

This method offers cost-effectiveness and simplicity in manufacturing, with an estimated material cost of only $0.50 per balloon. As described here, the manufacturing process is easy to follow, making balloon tag production accessible to anyone.

Protocol

1. Acid/base encapsulation

1. Mix a 1:2 ratio by the weight of H₂C₂O₄ (oxalic acid) and NaHCO₃ (sodium bicarbonate) in a mixing cup (see Table of Materials). If the acid-base powder mix is crystallized, grind it down using a mortar and pestle (Figure 1A).
2. Retrieve the size 3 vegetable-based capsules and the semi-automatic capsule filling machine to begin the process (see Table of Materials).
3. Place the cap sheet flat on a clean, dry surface. Align the encapsulation sheet on top of the cap sheet using the black pegs to fix it correctly in place (Figure 1B).
4. Separate the capsule tops and bottoms, unless using pre-separated capsules. The size #3 vegetable capsules, when closed, have overall dimensions of 15.9 mm in length, 5.57 mm in outer diameter (OD), 0.30 mL in volume, and weigh 47 mg.
5. Pour capsule tops into the encapsulation sheet (Figure 1C). Gently shake the tops into the holes with a circular motion. While doing this, cover the gap in the wall of the encapsulation sheet with one hand or a powder spreader to avoid spilling the tops (Figure 1D).
   1. Once the holes are filled, pour the excess capsule tops into a clean cup (Figure 1E). Identify any upside-down capsule tops and turn them over (Figure 1F). Ensure that all capsule tops are facing the correct direction in the cap sheet. It is important to ensure proper orientation, as incorrect alignment may result in capsule tops not properly joining with the capsule bottoms.
6. Remove the encapsulation sheet and set aside the filled cap sheet.
7. Take out the body or "bottom" sheet. Place it on a clean, dry, flat surface. Fix the encapsulation sheet to the bottom sheet, ensuring proper alignment by utilizing the black pegs to position it correctly in place.
8. Pour capsule bottoms into the encapsulation sheet and shake as before in a circular motion to fill the holes. Pour off excess capsule bottoms. Identify any upside-down capsule bottoms and turn them over.
9. Remove the encapsulation sheet from the bottom sheet and set it aside.
10. Pour the acid/base powder mixture onto the filled bottom sheet (Figure 1G). Use a plastic spreader to fill the capsule bottoms with the powder (Figure 1H). Check that all the capsule bottoms are filled (Figure 1I). Remove any unused acid/base powder.
11. Place the cap sheet on a flat surface and position the middle sheet on top, aligning it with the black pegs to ensure a correct fit. Ensure to line up all the capsule tops with the corresponding holes in the middle sheet.
12. Invert the cap sheet with the affixed middle sheet and align it with the filled bottom sheet (Figure 1J).
13. Gently press down on the cap sheet equally on all sides to join the tops and bottoms, fitting both sides of the capsule together (Figure 1K).
14. Remove the cap sheet and middle sheet from the bottom sheet. At this point, the capsule bottoms and tops should be properly joined together.
    1. Verify that each capsule top and bottom are fitted tightly; if not, manually press the capsule top and bottom together to create a tight fit. Remove the filled capsules and place them in an airtight, sealable container (Figure 1L).
       NOTE: For safe handling, it is essential for users to wear personal protective equipment (PPE) and face protection. Adequate ventilation should be ensured, and precautions should be taken to avoid ingestion, inhalation, and contact with the substance on the skin, eyes, or clothing. Additionally, it is important to prevent the generation of dust. For detailed information regarding safety, please refer to the safety data sheet (SDS) for oxalic acid and sodium bicarbonate. To maintain the integrity of the acid/base capsules, it is advised to store them away from direct sunlight and high humidity. Store the unused capsules in a sealed, airtight container. As long as the capsules are kept dry and free from moisture, they can be used effectively to ensure optimal functionality.

2. Silicone stopper manufacture

1. Using a fused deposition modeling (FDM) 3D printer (see Table of Materials), print a mold plate using the STL file provided in Supplementary File 1.
2. Place a clear packing tape on the bottom side of the mold plate so that each opening is sealed (Figure 2A).
3. Mix a 1:1 ratio by weight (e.g., 50 g each of Part A and Part B) of the commercially available silicone mold material into a mixing cup (see Table of Materials). Using a disposable spoon, thoroughly mix the chemical compound for approximately 5 min, or until it has become uniform.
4. Place the mold plate with the packing tape over a piece of paper. The paper will catch any potential silicone spill from the mold plate.
5. Begin pouring the silicone mixture into each stopper hole, ensuring they are all filled (Figure 2B). Use a rubber squeegee to spread the silicone into each stopper hole (Figure 2C). Remove the leftover silicone mixture from the surface of the mold plate.
6. Let the rubber stoppers dry for 4 h. After making sure the stoppers have fully cured (e.g., the silicone mixture has completely dried and hardened), remove the tape from the back of the mold plate (Figure 2D), and then begin pulling the stoppers out of the mold (Figure 2E).
7. Remove any excess silicone attached to the stoppers (Figure 2F).

3. Balloon tag assembly

1. Carefully insert the piercing tool (e.g., straight dental pick) into the silicone stopper (Figure 3A) (see Table of Materials). Insert the piercing tool into a 15 G syringe needle and then remove the piercing tool from the silicone stopper, leaving only the 15 G needle inside (Figure 3B). The piercing tool will create a slit inside the silicone stopper without cutting or removing any material.
2. Cut a piece of 50 lb. fishing line (see Table of Materials) to a length of 150 mm. Insert the fishing line through the 15 G syringe needle and into the silicone stopper (Figure 3C).
   1. While carefully holding the stopper and the fishing line together, remove the 15 G syringe needle from the stopper's body, leaving the fishing line inside the stopper (Figure 3D). Ensure the fishing line lengths are even on both sides of the stopper.
3. Insert two acid/base-powder-filled capsules into a latex balloon (Figure 3E) (see Table of Materials). Expand the balloon opening using the rubber-band expansion tool (i.e., castration band pliers) and then carefully insert one silicone stopper into the balloon opening (Figure 3F), leaving the fishing line's two ends outside the balloon.
4. Place two O-rings (1.6 mm wide, 8.1 mm ID, see Table of Materials) onto the rubber-band expansion tool and expand them. Insert the neck of the latex balloon through the two expanded O-rings (Figure 3G). Carefully pull the two O-rings away from the rubber-band expansion tool, leaving them tightly wrapped around the balloon's neck, centered on the stopper (Figure 3H).

4. Balloon tag attachment to Sensor Fish caps

1. Put one end of the fishing line through one of the small holes in the Sensor Fish cap (see Table of Materials) and bring it through the large hole in the center of the cap (Figure 4A).
2. Tie the two ends of the fishing line together, leaving about 13 to 26 mm between the top of the cap and the base of the balloon. Use four overhand knots on top of each other when tying the fishing line.
3. Leave the extra fishing line attached, as cutting it too close to a knot could potentially cause the knot to come undone (Figure 4B).
4. Test the knot by gripping the fishing line on each side of the knot with the fingers and pulling as hard as possible. Be cautious not to pull too close to the balloon, as it could unintentionally tear the fishing line through the rubber stopper.

Results

A study was conducted to determine the optimal methods for manufacturing balloon tags, focusing on the volume and temperature of water injected into the balloon. The study examined various input parameters, including the inflation start time, full inflation time, deflation start time, and the volume of the balloon at full inflation. The study was conducted at a desk with an ambient temperature of 21 °C.

A total of 360 balloon tags were prepared for the study. The tags were divided into 36 sets...

Discussion

This study concluded that three-capsule balloon tags injected with 5 mL of water at 18.3 °C had a slower start inflation time and consistently larger volume compared to two-capsule and four-capsule balloon tags. When the balloon tags were injected with water at 12.7 °C, the average volume was smaller, and the inflation time was longer. The three-capsule begins deflating first, followed by the four-capsule, and lastly the two-capsule. The inflation and deflation periods associated with each water temperature can...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3D Printed Silicone Stopper Plate	NA	NA
ARC800 Sensor Fish	ATS	NA
FDM 3D printer	NA	NA
Manual Capsule Filler Machine CN-400CL (Size #3)	Capsulcn	NA
Mold Star 15 SLOW	Smooth-On	NA
Oil-Resistant Buna-N O-Ring	McMaster-Carr	SN: 9262K141
Oxalic Acid, 98%, Anhydrous Powder (C2H2O4)	Thermo Scientific	CAS: 144-62-7
Rubber Band Expansion Tool	iplusmile	NA
Separated Vegetable Cellulose Capsules (Size #3)	Capsule Connection	NA
Smiley Face YoYo Latex balloon	YoYo Balloons, Etc.	NA
Sodium Bicarbonate Powder (CHNaO3)	Sigma	CAS: 144-55-8
Spectra Fiber Braided Fishing Line (50 lbs.)	Power Pro	NA