Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 175

Larval fish nutrition is a relatively new area of focus for both aquaculture and conservation efforts. Larval fish grow rapidly, with reports of 30–100% growth/day in some species, and their nutrient requirements are likely different from adult and juvenile stages (Hamre et al. 2013).

The composition of the egg from which a larval fish emerges is clearly significant for long‐term success. While egg composition varies dramatically between species, a few generalizations may be made based on the limited data available. Egg lipid levels tend to correlate positively with egg incubation times (Kaitaranta and Ackman 1981; Jaroszewska and Dabrowski 2011). Free amino acids, which are found in relative abundance in eggs, tend to be higher in eggs from pelagic fish than demersal fish (Jobling 2016). Larval fish usually depend on their yolk sac for three to five days post‐hatch, but this period may last up to 60 days in some species (Jaroszewska and Dabrowski 2011). Appropriate egg and yolk nutrition is modulated through the broodstock. Following the yolk‐sac period, larval fish transition to exogenous diet items. Mixed feeding, in which larval fish are offered food items while yolk‐sac nutrition is still available, is recommended to improve overall nutrition and stimulate gut development (Jaroszewska and Dabrowski 2011).

Options for feeding larval fish include live food items and commercial diets. Diets for small fish larvae are typically based on brine shrimp nauplii and rotifers (particularly Brachionus spp.). They may also be fed commercial microparticulate diets with hydrolyzed protein (a source of free amino acids), as the larvae may not possess the anatomy or physiology to break down more complex food particles (Kaushik et al. 2011; Langdon and Barrows 2011). However, these are associated with several issues, including high rates of nutrient loss due to large surface area, clumping, and poor uptake by larval fish (Langdon and Barrows 2011; Hamre et al. 2013). For larger larvae, live food items may include adult brine shrimp, copepods, and a variety of commercial diets. Live foods should always be enriched prior to feeding as this can significantly improve larval survival (Hamre et al. 2008; Dhert et al. 2014).

Nutrition of the broodstock impacts larval success. For example, vitamin E supplementation improved spawning quality in several fish species, and recommended levels were >150–190 mg D,L‐α‐tocopherol/kg diet (165–209 IU vitamin E/kg diet) (Fernández‐Palacios et al. 2011). Tryptophan also seems to be required at higher levels for reproduction than for growth (Jobling 2016). And in cod, egg fatty acid concentrations, particularly AA, DHA, and EPA concentrations, were positively correlated to hatching success (Pickova et al. 1997). The timing of critical broodstock nutrition can span a few weeks to several months, depending on when vitellogenesis occurs in the species (Fernández‐Palacios et al. 2011).

In fish species that show parental care, energy requirements are likely increased due to nest defense, cleaning, and/or oxygenation (e.g. tail fanning). A reduction in food intake may also occur during parenting. The condition of the parents can have significant consequences on the success of their offspring. For example, male smallmouth bass (Micropterus dolomieu) show parental care and when supplemented with additional food during this period, they show lower nest abandonment and improved reproductive success compared to males with no supplemental feeding (Zolderdo et al. 2016).