Interesting research or just bad science?

Male Maylandia greshakei. Image from https://de.wikipedia.org/.

Do you feed your cichlids commercial foods that contain probiotics? Many of the larger market food brands (e.g., New Life Spectrum, Cobalt) and even some smaller ones (e.g., AquaLife) offer probiotic infused foods espousing the benefits to fish digestion.

I came across a recent study (October 2017) in the World Journal of Pharmaceutical Research that looked at the effects of probiotics on reproduction.

Using juvenile Maylandia greshakei, a Lake Malawi mouthbrooder, as the model organism, the study divided the fish into five groups (1 control and 4 experimental). Each experimental group, labeled V1 through V4, was fed a commercially produced probiotic, called Vibact, using four different concentrations.  The measured weight of Vibact fed to each group, beginning with V1, was .2g, .4g, .6g, and .8g, respectively. According to the journal article, each Vibact tablet contained the following bacteria:

  • Streptococcus faecalis (30 million),
  • Clostridium butyricum (2 million),
  • Bacillus mesentericus (1 million),
  • Lactic acid bacillus (50 million).

The four experimental groups were fed three times a day over a 60 day period, and the study focused on measuring the following:

  • Relative Fecundity (RF),
  • Gonadosomatic Index (GSI) (simply measuring the mass of the gonads in proportion to the body mass),
  • fry survival,
  • dead fry,
  • deformed fry,
  • weight and length of fry,
  • and weight and length of adult

Below I’ve reproduced one of the results tables in the journal article.

Experiment Groups Experimental Groups
V0 (control) V1 (.2g) V2 (.4g) V3 (.6g) V4 (.8g)
Fecundity 14.23±6.19c 18.14±9.19ab 22.13±9.89a 19.7±8.36ab 17.21±9.2b
Fry survival 11.71±4.71c 16.12±8.12b 21.11±8.23a 17.82±7.65ab 15.85±9.31b
Dead fry 2.46±2.18b 1.83±1.76a 1.03±1.27a 1.64±1.32a 1.15±1.31a
Deformed fry 0.30±0.74b 0.22±0.52ab 0.3±0.32a 0.14±0.34ab 0.20±0.53ab
Weight (g) 0.69±0.06ab 0.74±0.11c 0.76±0.04a 0.71±0.12ab 0.68±0.10b
Length (mm) 38.16±1.03a 39.56±1.83b 41.31±1.10a 39.67±1.14a 39.37±1.11a
Fry weight (g) 0.0018±0.0001b 0.0024±0.0002a 0.0026±0.003a 0.0023±0.0002a 0.0022±0.0002a
Fry length (mm) 5.32±0.63d 6.11±0.51a 6.38±0.53c 6.19±0.56ab 6.14±0.63bc
GSI 8.11±0.42b 9.38±0.39a 9.67±0.54a 9.4±0.4a 8.81±0.30ab

When I first looked at these results, I thought they were rather intriguing. Most aquarists think of probiotics as only something that is beneficial to fish digestion. The results of this research, however, suggest probiotic supplements may have additional benefits (e.g., producing higher fecundity, lower fry mortality, faster fry growth).

On the other hand, once I read the article, I started to question the study. The details of the research, in my opinion, are both lacking and inconsistent. For example, in one section of the article, it states that the experimental feeding was three times a day. However, a bit further down in the “Experimental design” section, it states the experimental fish were fed twice a day.

In addition, the study claims the experimental fish were ~4 month old juveniles at 3-4 cm in length. Part of the research included measurements of offspring, which means each group of the experimental fish would have had to spawn. If the study fish were indeed juveniles, then they weren’t mature enough to breed.  I don’t think I’ve ever seen 3-4 cm mbuna cichlids breed. Other than a 15-day acclimation period for the experimental fish in the research lab and the 60 day experimental period, no other details are provided about how long the fish resided at the laboratory during the study. It’s possible there was a time gap in between acclimation and experimentation, but that isn’t clear. Even if there was no time gap, I question the accuracy of 3-4 cm cichlids becoming mature enough to breed during the experiment.

Furthermore, the article states that the fish were divided into five study groups (1 control and 4 experimental). However, the gender distribution and numerical composition (n=?) of each group is omitted from the details. A carefully controlled experiment of this kind would have the same distribution of genders and same number of fish per study group, yet those details are completely left out.

Making matters even worse, the article states that Maylandia greshakei may reach 1 meter in length. That is patently false. The maximum length of Maylandia greshakei is ~6 inches (~16 cm)I’m willing to conclude that error was a typo, but when coupled with the additional details (or lack thereof) about the experimental design, my confidence in the results isn’t high. There are just too many problems with this research for me to accept the results. Checking out the details of the journal itself reinforces my opinion.

Citation:
Ambika, P., J. Ronald, A. Pushparaj. “Application of dietary probiotic (Vibact) level on reproductive performance in Ice Blue cichlid (Maylandia greshakei).” World Journal of Pharmaceutical Research. Volume 6, Issue 15, 1040-1048. 2017. DOI: 10.20959/wjpr201715-10159.

You can retrieve a copy of the article here – https://www.wjpr.net/index.php/download/article/1510824097.pdf

 

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