Shieh-Tsung et al. (2015) investigated the benefits of diets containing Daphnia similis meal. Daphnia is considered to be a source of
nutrient-rich food with high protein content. Further, the carapace and the
resting eggs of Daphnia contain a
high amount of chitin and chitosan. Previous studies have shown that chitin and
chitosan are both effective in immune stimulation and disease resistance for
aquaculture organisms.
Asian seabass larvae were fed with
three different experimental diets. Diets contained 0% (control), 5% (D5) and
10% (D10) Daphnia meal. Fish meal and
fish oil decreased in the diets D5 and D10 as the amount of Daphnia meal increased.
All three experimental treatments
were challenged with the pathogenic bacteria Aeromonas hydrophila to examine the disease resistance. Further, non-specific immune parameter were
measured. Mx gene expression in the spleen and head kidney were analysed by using
real-time PCR with SYBR green to examine target mRNA.
Daphnia meal
had no negative effects on the general survival rate of the larvae. All three
treatments showed no significant difference in survival after being fed for 42
days. Final weight, feed efficiency and percentage weight gain showed no
significant difference between the control and D5 treatments as well. Only D10
treatments had a significant lower final weight, percentage of weight gain and
feed efficiency. Apparently the lack of nutrients in D10 due to less fish meal
caused a worse growth performance.
Daphnia meal showed a positive
effect on resistance to A. hydrophila. The mortality rate of fish larvae
was highest in the control treatment and decreased with higher Daphnia meal addition. Further,
respiratory burst activity increased in D5 and D10 treatments with D10 having
the highest rate. Phagocytic activity increased as well in Daphnia meal treatments, but this time with D5 treatments having
the highest rate. Mx proteins which are expressed in response to viral
infection also increased in Daphnia
meal treatments. All in all the author suggest that a diet containing 5%
Daphnia meal is suitable for further use since it has no negative impact on
growth performance, though showed significant improvement in non-specific
immunity and resistance.
I think the findings are promising with
a potential for further use. It would be interesting to combine the gut
bacteria of Debasis et al. (2015) and
the Daphnia meal to see if that would
have an even bigger positive effect. Although, one problem I could think of is
the high amount of chitin, since some Vibrio
species have a preference for organisms with chitin.
Chiu, Shieh-Tsung;
Shiu, Ya-Li; Wu, Tsung-Meng u. a. (2015): „Improvement in non-specific
immunity and disease resistance of barramundi, Lates calcarifer (Bloch),
by diets containing Daphnia similis meal“. In: Fish & Shellfish Immunology. 44 (1), S. 172-179, DOI: 10.1016/j.fsi.2015.02.002.
Hi Nuri,
ReplyDeleteI was also going to pick up on the Vibrio issue you mentioned at the end! How much of an issue do you think it would be in this instance? Was there any mention of how the Dapnia were collected for this experiment, were they grown in labs? If so I think the Vibrio attachment thing would probably not be too much of an issue as the Daphnia would likely be grown aseptically (or at least as aseptically as possible) and unless there were vibrios present in the waters which the larvae were being grown in I guess this could be overlooked?
Hi Laura,
Deletethe Daphnia were acquired from a live food culture farm. I assume that the risk of infection at this step can be excluded, since they must have high safety standards. The fish were reared in cement tanks around 30 km away from the coastline. They didnt mention if the tanks were indoor or outdoor. Anyway, I doubt that there is a chance of bacterial infection via marine aerosols. Moreover was the meal prepared by drying the Daphnia at 60°C. Vibrios might no infect dried dead hosts at all. All in all I have to agree with you, that the likelihood of an Vibrio infection under these conditions is very unlikely.
It would be interesting to apply the Daphnia meal treatment on other fish species which a farmed under different conditions. However, I wouldn't apply the Daphnia meal treatment in open ocean fish farms.
Hi Nuri, this is really interesting. There seems to have been a lot of recent work looking at the effects of chitin and chitosan on fish, especially Asian Seabass, of which the majority seems to have a positive impact. Fewer studies, however, seem to have looked into the positive effects of the compounds against growth rate which is obviously important in aquaculture.
ReplyDeleteDo you think the negative effects on growth are specific to the daphnia? There are multiple sources of chitin and chitosan, other studies have used sources from shrimp shells, insect species and even fungus which could contain other useful nutrients, or their use could prevent the material going to waste (shrimp shells).
It would be interesting to evaluate and compare a number of sources to ascertain if there is a particular source which has additional nutritional qualities, is cheap and safe to produce or could prevent commercial waste giving it economic and environmental importance.
Hi Katherine,
Deletethere was only a negative effect on growth with the 10% Daphnia meal diet. 5% Daphnia meal had even a slightly higher final weight than the control, though not statistically significant. Decrease in growth, final weight, feed efficiency amd percentage of weight gain in the D10 groups was most likely caused by unbalanced nutrient content in Daphnia meal. The author mentioned a very low rate of the essential amino acid methionine in the Daphnia meal (Daphnia meal: 0.84%; Fish meal: 2.51%). Since the amount of fish meal decreased with incresed Daphnie meal was that most likely the main reasion for the decreased growth factors.
I think the key of a future high quality diet with promising growth rates and low infection rates would be a combination of e.g. Daphnia meal and the gut bacteria by Debasis et al. (2015). You would have an improved immune system by the Daphnia meal and a better growth performance due to the gut bacteria which also led to competitive exclusion of Vibrios. The main goal for responsible aquafarming should be a reduction of antibiotics and fish meal by being still economically competitive at the same time. This studies are a first step in the right direction.