Good morning everyone,
For experimental purposes, I am trying to establish a non-aseptic cultivation of Myriophyllum spicatum in my laboratory.
The cultivation conditions (both for the aqueous medium and sediment) are the same as those described in OECD Test Guideline No. 239.
The plants are growing in a 40-liter aquarium maintained at 18°C. The aquarium is equipped with a pump that functions as both a filter and an aerator. Additionally, it has a commercial aquarium lamp set to a photoperiod of 16 hours of light and 8 hours of darkness.
My goal is to establish the culture in conditions as close as possible to those specified in OECD TG 239.
However, I’m facing an issue:
A few weeks after initiating the culture, a slimy, transparent white biofilm began to grow on various surfaces, particularly on the plants and sediment. This biofilm has been expanding to the point of inhibiting plant growth and likely interfering with photosynthesis.
I’m aware that aquariums need time to cycle and develop a stable bacterial community to degrade organic matter. However, in my case, the bacterial bloom seems excessive.
At the moment, I am attempting the following routine maintenance measures on a weekly basis:
Cleaning the filter sponges
Replacing 10–20% of the water
Manually removing the biofilm and any decaying leaves
Exposing the water to UVC light
I suspect that decomposing organic material might be fueling this bacterial overgrowth.
Do you have any experience or suggestions for cultivating M. spicatum under these conditions?
How can I better control the accumulation of organic debris and maintain a clean, healthy environment for the plants?
Additionally, I’ve noticed that the plants tend to lose their lower leaves. Could this be due to insufficient light intensity or a lack of micronutrients? (I’m aware that the sediment and medium from OECD TG 239 might not provide all essential micronutrients.) Or is this typical behavior for M. spicatum under certain conditions?
Any advice that could help me achieve a thriving and stable culture would be greatly appreciated.
I've also noticed that my plants grow really thin and of a pale green. Maybe too few light? The PAR value at the level of the upper part of the pots range between 54 and 77 umol/m^2/s
Thank you in advance for your support
Hello, Giambattista Carluccio
Your setup aligns well with OECD Test Guideline No. 239, and the challenges you're encountering—biofilm formation, leaf loss, and pale growth—are common in early-stage aquatic macrophyte cultures.
Here are targeted recommendations based on ecotoxicological and microbiological principles
The slimy, transparent biofilm is likely a result of heterotrophic bacterial overgrowth fueled by decomposing organic matter and possibly excess dissolved organic carbon (DOC). While some biofilm is expected during tank cycling, excessive accumulation can inhibit light penetration and photosynthesis.
Recommendations:
• Pre-rinse sediment before use to reduce labile organic content.
• Introduce fast-growing submerged plants (e.g., Elodea canadensis) temporarily to compete for nutrients and stabilize microbial communities.
• Add a small population of benthic grazers (e.g., Physa spp. snails or Gammarus spp.) to help control biofilm without disrupting the test system.
• Reduce feeding or organic inputs if any are present unintentionally (e.g., decaying leaves).
• Consider a slow-release carbon filter or activated carbon to adsorb excess DOC.
• UVC exposure is helpful but should be intermittent to avoid disrupting beneficial microbial succession.
Light Intensity and Photomorphogenesis
PAR values of 54–77 µmol/m²/s are on the lower end for submerged macrophytes. M. spicatum typically thrives at 100–200 µmol/m²/s under laboratory conditions. Pale, thin growth and lower leaf abscission suggest suboptimal light for photosynthetic efficiency and apical dominance.
Recommendations:
• Upgrade to full-spectrum LED lighting with PAR ≥120 µmol/m²/s at canopy level.
• Ensure uniform light distribution across the tank to prevent phototropic stress.
• Monitor chlorophyll fluorescence (Fv/Fm) if possible, to assess photosynthetic health.
Nutrient Optimization
OECD TG 239 sediment may lack trace elements like Fe, Mn, Zn, and B, which are critical for vascular plant development. Lower leaf senescence and chlorosis often indicate micronutrient deficiencies.
Recommendations:
• Supplement with a chelated micronutrient mix (e.g., Seachem Flourish Trace or custom Hoagland's solution minus nitrogen/phosphorus if already present).
• Use root tabs near plant bases to localize nutrient delivery.
• Avoid over-fertilization, which can exacerbate microbial blooms.
Plant Morphology and Adaptation
Lower leaf loss is typical in M. spicatum under shaded or nutrient-poor conditions. The plant reallocates resources to apical growth when basal tissues are no longer photosynthetically viable.
Recommendations:
• Prune apical shoots periodically to encourage lateral growth and reduce shading.
• Ensure sediment depth and anchorage are sufficient to support root uptake and stability.
Giambattista Carluccio,
Your maintenance routine is sound, and with slight adjustments to light intensity, nutrient supplementation, and microbial control, you should see improved vigor and stability in your M. spicatum culture. If you're conducting toxicity assays, ensure that any interventions (e.g., grazers or supplements) are accounted for in control setups.
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