The growth and development of healthy culture subjects are essential in increasing productivity in the aquaculture industry. A primary determinant of aquatic animal productivity is the ambient microbial population. If an aquatic animal's microbiome is diverse, with bacteria favoring beneficial over pathogenic species, the health and growth of the animal (i.e., fish or crustacean) can be substantially improved. Embryonic and newly hatched Zebrafish Danio rerio larvae were reared in the presence of (1) water from the broodstock culture tank as a control, (2) a probiotic solution containing 19 strains of live lactic acid bacteria (LAB), or (3) an antibiotic (AB) solution with amoxycillin. Developmental parameters were monitored until 10 d postfertilization. Bacteria present in the water and larvae were cultured and identified by sequencing the V4 hypervariable region of bacterial 16S ribosomal RNA. Probiotic‐treated larvae showed significant increases in every measured morphological parameter and in survival compared to the controls and AB‐treated larvae, including TL, eye development, and swim bladder development before first feeding. Staining with DASPEI (2‐(4‐[dimethylamino]styryl)‐N‐ethylpyridinium iodide) produced fluorescence, revealing increased mitochondrial activity in the gastrointestinal tracts of probiotic‐treated larvae and reflecting advancement of initial metabolic function. Probiotic‐treated larvae showed accelerated yolk absorption, resulting in increased nutrient mobilization and growth. Microbial analyses revealed a greater concentration of bacteria in larvae in response to the probiotic treatment compared to the other two treatments. Species identified in all three treatments included Pseudomonas spp. and Aeromonas spp. (Proteobacteria). The second most diverse and abundant microbiome was seen in controls, whereas AB‐treated larvae had the least diverse microbiome. All treatments revealed the presence of proteobacteria, but an AB‐resistant pathogenic bacterium (Stenotrophomonas maltophilia) was identified in the AB group. These results reveal that the presence of LAB and other bacteria favorably influenced early larval growth, development, digestive function, and survival in Zebrafish even before the onset of feeding.

Iodine imparts protective antioxidant actions that improve the fitness of invertebrate organisms, and peptides carrying iodine initially appear to have served in a defensive capacity. Tyrosine carries multiple iodines in some echinoderms, and these peptides transferred to progeny serve both protective and signaling purposes. This parental relationship appears to be the most likely evolutionary basis for emergence of the vertebrate thyroid endocrine system, and its critically important development-promoting actions in larval and (later) fetal ontogeny. Thyroxine (T4) and Triiodothyronine (T3) induce settlement and stimulate transitions to alternative feeding modes in some echinoderms. This transgenerational relationship has been conserved and elaborated in vertebrates, including humans, which share common ancestry with echinoderms. Thyroid insufficiency is damaging or can be lethal to larval fishes; egg yolk that is insufficiently primed with maternal thyroid hormones (TH) results in compromised development and high mortality rates at the time of first-feeding. Maternally-derived TH supplied to offspring supports the onset of independent feeding in fishes (eye, mouth, lateral line, swim bladder and intestinal maturation) and survival by comparable developmental mechanisms in placental mammals. Fishes evolved precise control of TH secretion and peripheral processing; early metamorphic and feeding mode actions were joined by controlled thermogenesis in homeotherms.

Microbial diversity within an aquatic community can be used to increase the growth and development of organisms. In this study, Zebrafish larvae were reared in three treatments 1) a probiotic containing 17 strains of Lactobacillus spp., 2) an amoxicillin solution, 3) water from the broodstock culture tank as the control. Survival of the larvae throughout 10 dpf was recorded. To determine the development of the gastrointestinal tract DASPEI stain was used for larvae at the age of 3 dpf to 6dpf. The intensity of the fluorescence in each larva was observed through the automated digital microscope. According to the experiment results, a significant difference (P<0.0001) in the survival rates among all treatments was recorded. The probiotic-treated larvae (PTL) had a higher survival rate. This could be due to the presence of lactic acid bacteria in the probiotic treatment, which helps in enhancing immunity. In DASPEI staining, also PTL exhibits more fluorescence in the GI tract at 24 hours to 48 hours post-hatch than the other two treatments. The main possible reason behind this could also be the presence of Lactobacillus spp. Which directly influences the higher activity of the digestive system.