Role of heterotrophic protists in first feeding by cod (Gadus morhua) larvae

Abstract

The present study evaluated whether the presence of autotrophic phytoplankton and/or heterotrophic dinoflagellates (Oxyrrhis marina) influenced first-feeding success and early larval growth and development of Baltic cod Gadus morhua L. Newly hatched cod larvae were maintained in salt water ('clear water', CW), greened water using Nannochloropsis sp. (NA) or a combination of Nannochloropsis sp. and O. marina (NO) from 2 to 11 d post-hatch. On each day, larvae from each group were placed into feeding tanks and provided potential prey (nauplii of the calanoid copepod Acartia tonsa). Feeding performance was measured both as the percentage incidence of feeding and gut fullness index. The onset of first feeding, point of no return and the magnitude of feeding were derived from the feeding incidence. The study clearly demonstrated precocious, exogenous feeding by cod larvae in the presence of Nannochloropsis sp. and O. marina by 1.2 and 2.2 d (10°C), respectively. Gut fullness was also significantly improved in the presence of both phytoplankton and protists over the entire window of opportunity (defined as the period between onset of first feeding and point of no return). However, the nutritional capacity of these unicellular organisms was not sufficient to alter the somatic growth characteristics in NA and NO groups relative to starving yolk-sac larvae maintained in only salt water (CW group). These findings expand the current understanding of the degree of interaction between fish larvae and unicellular plankton communities and indicate a lack of nutritional benefits from feeding on components of the pelagic microbial loop but a clear benefit in terms of 'priming' first-feeding capabilities.KEY WORDS: Protists · Marine fish · First feeding · Larvae · Cod · Oxyrrhis marina · Nannochloropsis sp. · Survival · Growth 410: 197-204, 2010 plankton is fed on by heterotrophic zooplankton that, in turn, is preyed upon by fish larvae. Analyses of larval fish gut contents and feeding behaviour has resulted in the claim that herbivorous, crustacean zooplankton (copepods) is the preferred prey of young marine fish larvae (Munk 1997, Pepin & Penney 2000. However, recently there has been some evidence to suggest a potential flexibility in the feeding behaviour of fish larvae (Pepin & Dower 2007). In particular, more focus has been given to representatives of the planktonic microbial loop. For example, marine fish larvae have been reported to directly feed on heterotrophic protists (Lasker 1975, Scura & Jerde 1977, Fukami et al. 1999, organisms that can be highly abundant in marine environments during specific time periods (Tamigneaux et al. 1997, Hansen & Jensen 2000, Sommer et al. 2002, Ptacnik 2003. However, it is still largely unknown if indirect (incidental) or direct ingestion of algae and heterotrophic protists provides any nutritional and/or energetic value for marine fish larvae. Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerEvidence exists from marine fish larvi...

Food and feeding of Argentine hake (Merluccius hubbsi) larvae in the Patagonian nursery ground

“…Moreover, this fact would reduce the competition for resources with anchovy (Engraulis anchoita) first-feeding larvae that also nurse in the area and prey exclusively on copepod eggs and nauplii due to a mouth gape limitation (Viñas and Ramírez, 1996). Besides copepod eggs and nauplii, there is growing evidence that soft organisms such as heterotrophic protists, which are undetectable with standard larval gut content studies, can play an important role in larval nutrition, either through consumption or indirectly due to their presence (de Figueiredo et al, 2007;Fukami et al, 1999;Overton et al, 2010). Thus, further studies considering alternative techniques, such as the fatty-acid trophic markers or stable isotopes approaches, should be carried out to establish the importance of these prey items in hake larvae diet, as has been previously done for different species (Pepin and Dower, 2007;Rossi et al, 2006).…”

On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles

“…In their laboratory study, cod larvae~12 mm SL had the highest potential for growth but also starvation-induced mortality. In contrast, first-feeding cod yolk-sac larvae have been demonstrated to have a higher potential to withstand periods of prey deprivation (Overton et al, 2010). Other studies conducted on marine fishes (e.g., Bochdansky et al, 2008) reveal that larvae may pass through multiple "critical periods" where starvation resistance and growth capacity are linked.…”

“…Overton et al (2010) estimated the window of opportunity for Baltic cod yolk-sac larvae in the laboratory to be 5.6 days at 10°C (56 Dd). At warmer temperatures (19°C), Yúfera et al (1993) estimated the window of opportunity to be only 2 days (38 Dd) for sea bream.…”

Latitudinal and taxonomic patterns in the feeding ecologies of fish larvae: A literature synthesis

“…Diet results from all studies were based on gut 384 content analysis, which, though relatively simple and straightforward, is an informative 385 technique that allows for the enumeration of prey and their identification to an often low 386 taxonomic level-but only when those prey are observable. There is growing evidence that 387 organisms that go unnoticed or are altogether unnoticeable (particularly heterotrophic protists) 388 can play an important role in larval nutrition, either through consumption or indirectly due to 389 their presence (de Figueiredo et al, 2005;Overton et al, 2010;Pepin and Dower, 2007). 390…”