BOWEN: I have not compared it with fish meal, but I have compared it with the essential
amino acid requirements of warmwater fish given in the literature and it is more than
adequate to meet these.
MORIARTY: Another point on that of course is that the protein content of microalgae
and bacteria is very high compared with that of other plant material. It is around 50 to
60% of the dry weight. This varies of course.
BOWEN: Yes, there are very few storage compounds, such as carbohydrates, in blue-
green algae and bacteria and instead of storing energy, these cells continue to reproduce,
making more protein.HENDERSON: You mentioned that there are data for assimilation efficiencies of grass
carp feeding on plant protein.BOWEN: Yes, these are around 50%.JALABERT: Is there any evidence of feeding rhythms?MORIARTY: My experience of the Lake George fish is that they feed during daylight
hours only. They start feeding at dawn or just before. (Editor's note: Whyte (1975) ,
reported that Sarotherodon galilaeus multifasciatus and Tilapia busumana in Lake Bosum-
twi, Ghana, both feed at night. The water of this lake is very clear.)JALABERT: Does the efficiency of the food utilization vary according to the time at
which it is eater. during the day? For example it has been shown in some fish, particularly
catfish, that the efficiency of food utilization is not the same in the morning as in the
afternoon.CAULTON: Yes, we have shown that with the acid secretion cycle in the tilapia. Until
you have acid production in the stomach sufficient to lyse the food items, you will not
get any release of nutrients. So the first portion of the meal ingested in the morning is
hardly digested at all, and there is a large increase in efficiency as the day progresses.BOWEN: I have actually worked that out by counting the number of empty diatom
frustules at different locations in the gut. There is a group of undigested diatoms which is
derived from the first part of the daily meal but this is not a very significant portion of
the diet and the digestive system becomes efficient very rapidly. So that there is 10% or
less of the food that is not fully digested and the remainder is very effectively digested.
NASH: In this detritus, is there any gelatinous material? There seems to be a nice parallel
between this freshwater situation and that sometimes found in saline waters. For example,
there are some excellent feeding grounds for marine shrimp in Brazil in the Cabo Frio
area, and excellent feeding grounds for milkfii in many of the Pacific low atolls where
the substrate is a deposit of blue-green algae and detritus, but both are characterized by
being very gelatinous. The substrate is similar to the lab-lab prepared in the Philippine
milkfish ponds which again has a very high protein level.
BOWEN: Is this gelatinous appearance the result of a large mass of blue-green algae?
NASH : I don't know what it is.
LOVSHIN: There are some blue-greens which form gelatinous masses.
BOWEN: I know that some diatoms secrete gelatinous strands which tend to bind them
together into a fine substrate, but I don't know if blue-greens do that.
MORIARTY: Many benthic and planktonic blue-green algae secrete large amounts of
slime. Its nutritive value for fish has not been assessed, but it may well be utilized.