Greenwater Technique

Greenwater is a technique of adding microalgae to your system as an enhancement, not as a direct food source. The most commonly used microalgae for creating greenwater is Nannochloropsis. Pavlova and Isochrysis can also be used if there is adequate circulation to keep these larger cells in suspension.

The results of using greenwater are significant - reduced mortality and better fish health. The reasons why greenwater works are not so well proven. Hatchery managers believe that Greenwater produce these effects:

  1. Enhancing visual contrast and light dispersion - i.e. the fish can see better. This improves food detection and location, and reduces "nose bumping" syndrome (which leads to bruising and disease). Recent studies indicate that green is the first color that develops in larval fish eyes which might explain the enhanced visual contrast.
  2. Improved nutrition through direct digestion.
  3. Improved nutritional value of live prey (rotifers, brine shrimp, etc.) in the tank which consume the microalgae.
  4. Stabilization of the water quality by removing metabolic products and producing oxygen.

In outdoor ponds there is an additional benefit of Greenwater for reducing sunlight. Many animals prefer to live in a darker environment and do not do well in bright, clean water. Greenwater is used to darken the water which reduces the stress and mortality of the animals.

Instant Algae® has been used for Greenwater in hatcheries and aquariums around the world. Although the cells are not live they stay well suspended in the water column with minimal circulation. Instant Algae® microalgae provides all the listed benefits of Greenwater except the last (#4 - producing oxygen) which can only be done by using live algae.

Dosage: Greenwater using Nannochloropsis is often applied at 30 million cells / ml. For each 1000 liters of greenwater you will need 11 ml's per day. The algae should be divided and applied several times during the day as it will be constantly consumed by rotifers.

Greenwater Articles:

DEVELOPMENT OF THE PH IN THE INTESTINAL TRACT OF LARVAL TURBOT
K. Hoehne-Reitan, E. Kjørsvik, K.I. Reitan-2001
Marine Biology, 139(6): 1159-1164
Abstract:
The pH in the gut of turbot larvae and juveniles of turbot was studied from day 11 until the completion of metamorphosis. Dietary effects on the gut pH were estimated when larvae were offered live feed, a microdiet, only microalgae or no feed. The pH in the gut was weakly alkaline until day 24 after hatching with no differences between the foregut, midgut and hindgut. The foregut contents started to turn acidic from day 28 after hatching when the larvae were already weaned successfully, which indicates that an acidic pH is not necessary for the digestion and utilisation of formulated feed. During the following 20 days the pH in the foregut/stomach decreased further to a minimum of pH 3.5, while the pH in the midgut and the hindgut increased slightly to a maximum of pH 9.0. Larvae receiving live feed, microdiet or microalgae had a similar pH in the midgut on day 11, while starved larvae exhibited a lower gut pH. This suggests bicarbonate secretion from the larval pancreas stimulated by ingested microalgae or feed particles.
(Norwegian University of Science and Technology (NTNU), Department of Zoology, Brattøra Research Centre, 7491 Trondheim, Norway, Tel: +47-73-590321, Fax: +47-73-596311, E-mail of K.I. Reitan: Katja.Reitan@chembio.ntnu.no)

Last updated 2003-12-28